Fix the type of copyWithin

Only the first parameter of copyWithin is required, contrary to the old type. This commit fixes that type to allow correct usage of the copyWithin
function. See [the usage of copy within](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/copyWithin).

Author: ericbf

src/lib/es2015.core.d.ts

@@ -33,15 +33,23 @@ interface Array<T> {
     fill(value: T, start?: number, end?: number): this;
 
     /**
-     * Returns the this object after copying a section of the array identified by start and end
-     * to the same array starting at position target
-     * @param target If target is negative, it is treated as length+target where length is the
-     * length of the array.
-     * @param start If start is negative, it is treated as length+start. If end is negative, it
-     * is treated as length+end.
-     * @param end If not specified, length of the this object is used as its default value.
-     */
-    copyWithin(target: number, start: number, end?: number): this;
+     * Return the `this` object after shallow copying part of the array to another location in the same array, without modifying its length.
+     * @param target Zero-based index at which to copy the sequence to, converted to an integer.
+     * - Negative index counts back from the end of the array — if `target < 0`, `target + array.length` is used.
+     * - If `target < -array.length`, `0` is used.
+     * - If `target >= array.length`, nothing is copied.
+     * - If `target` is positioned after `start` after normalization, copying only happens until the end of `array.length` (in other words, `copyWithin()` never extends the array).
+     * @param start Zero-based index at which to start copying elements from, converted to an integer.
+     * - Negative index counts back from the end of the array — if `start < 0`, `start + array.length` is used.
+     * - If `start < -array.length` or `start` is omitted, `0` is used.
+     * - If `start >= array.length`, nothing is copied.
+     * @param end Zero-based index at which to end copying elements from, converted to an integer. `copyWithin()` copies up to but not including end.
+     * - Negative index counts back from the end of the array — if `end < 0`, `end + array.length` is used.
+     * - If `end < -array.length`, `0` is used.
+     * - If `end >= array.length` or `end` is omitted, `array.length` is used, causing all elements until the end to be copied.
+     * - If `end` is positioned before or at `start` after normalization, nothing is copied.
+     */
+    copyWithin(target: number, start?: number, end?: number): this;
 }
 
 interface ArrayConstructor {

src/lib/es2020.bigint.d.ts

@@ -142,15 +142,23 @@ interface BigInt64Array {
     readonly byteOffset: number;
 
     /**
-     * Returns the this object after copying a section of the array identified by start and end
-     * to the same array starting at position target
-     * @param target If target is negative, it is treated as length+target where length is the
-     * length of the array.
-     * @param start If start is negative, it is treated as length+start. If end is negative, it
-     * is treated as length+end.
-     * @param end If not specified, length of the this object is used as its default value.
-     */
-    copyWithin(target: number, start: number, end?: number): this;
+     * Return the `this` object after shallow copying part of the array to another location in the same array, without modifying its length.
+     * @param target Zero-based index at which to copy the sequence to, converted to an integer.
+     * - Negative index counts back from the end of the array — if `target < 0`, `target + array.length` is used.
+     * - If `target < -array.length`, `0` is used.
+     * - If `target >= array.length`, nothing is copied.
+     * - If `target` is positioned after `start` after normalization, copying only happens until the end of `array.length` (in other words, `copyWithin()` never extends the array).
+     * @param start Zero-based index at which to start copying elements from, converted to an integer.
+     * - Negative index counts back from the end of the array — if `start < 0`, `start + array.length` is used.
+     * - If `start < -array.length` or `start` is omitted, `0` is used.
+     * - If `start >= array.length`, nothing is copied.
+     * @param end Zero-based index at which to end copying elements from, converted to an integer. `copyWithin()` copies up to but not including end.
+     * - Negative index counts back from the end of the array — if `end < 0`, `end + array.length` is used.
+     * - If `end < -array.length`, `0` is used.
+     * - If `end >= array.length` or `end` is omitted, `array.length` is used, causing all elements until the end to be copied.
+     * - If `end` is positioned before or at `start` after normalization, nothing is copied.
+     */
+    copyWithin(target: number, start?: number, end?: number): this;
 
     /** Yields index, value pairs for every entry in the array. */
     entries(): IterableIterator<[number, bigint]>;
@@ -414,15 +422,23 @@ interface BigUint64Array {
     readonly byteOffset: number;
 
     /**
-     * Returns the this object after copying a section of the array identified by start and end
-     * to the same array starting at position target
-     * @param target If target is negative, it is treated as length+target where length is the
-     * length of the array.
-     * @param start If start is negative, it is treated as length+start. If end is negative, it
-     * is treated as length+end.
-     * @param end If not specified, length of the this object is used as its default value.
-     */
-    copyWithin(target: number, start: number, end?: number): this;
+     * Return the `this` object after shallow copying part of the array to another location in the same array, without modifying its length.
+     * @param target Zero-based index at which to copy the sequence to, converted to an integer.
+     * - Negative index counts back from the end of the array — if `target < 0`, `target + array.length` is used.
+     * - If `target < -array.length`, `0` is used.
+     * - If `target >= array.length`, nothing is copied.
+     * - If `target` is positioned after `start` after normalization, copying only happens until the end of `array.length` (in other words, `copyWithin()` never extends the array).
+     * @param start Zero-based index at which to start copying elements from, converted to an integer.
+     * - Negative index counts back from the end of the array — if `start < 0`, `start + array.length` is used.
+     * - If `start < -array.length` or `start` is omitted, `0` is used.
+     * - If `start >= array.length`, nothing is copied.
+     * @param end Zero-based index at which to end copying elements from, converted to an integer. `copyWithin()` copies up to but not including end.
+     * - Negative index counts back from the end of the array — if `end < 0`, `end + array.length` is used.
+     * - If `end < -array.length`, `0` is used.
+     * - If `end >= array.length` or `end` is omitted, `array.length` is used, causing all elements until the end to be copied.
+     * - If `end` is positioned before or at `start` after normalization, nothing is copied.
+     */
+    copyWithin(target: number, start?: number, end?: number): this;
 
     /** Yields index, value pairs for every entry in the array. */
     entries(): IterableIterator<[number, bigint]>;