Add missing overloads to flow rune proposal

src/libraries/System.Private.CoreLib/src/System/Char.cs

@@ -129,16 +129,22 @@ public bool Equals(char obj)
             return m_value == obj;
         }
 
-        internal bool Equals(char right, StringComparison comparisonType)
+        /// <summary>
+        /// Returns a value that indicates whether the current instance and a specified character are equal using the specified comparison option.
+        /// </summary>
+        /// <param name="other">The character to compare with the current instance.</param>
+        /// <param name="comparisonType">One of the enumeration values that specifies the rules to use in the comparison.</param>
+        /// <returns><see langword="true"/> if the current instance and <paramref name="other"/> are equal; otherwise, <see langword="false"/>.</returns>
+        public bool Equals(char other, StringComparison comparisonType)
         {
             switch (comparisonType)
             {
                 case StringComparison.Ordinal:
-                    return Equals(right);
+                    return Equals(other);
                 default:
-                    ReadOnlySpan<char> leftCharsSlice = [this];
-                    ReadOnlySpan<char> rightCharsSlice = [right];
-                    return leftCharsSlice.Equals(rightCharsSlice, comparisonType);
+                    ReadOnlySpan<char> thisCharsSlice = [this];
+                    ReadOnlySpan<char> otherCharsSlice = [other];
+                    return thisCharsSlice.Equals(otherCharsSlice, comparisonType);
             }
         }
 

src/libraries/System.Private.CoreLib/src/System/SpanHelpers.T.cs

@@ -1464,6 +1464,10 @@ internal static bool NonPackedContainsValueType<T>(ref T searchSpace, T value, i
         internal static int IndexOfChar(ref char searchSpace, char value, int length)
             => IndexOfValueType(ref Unsafe.As<char, short>(ref searchSpace), (short)value, length);
 
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        internal static int LastIndexOfChar(ref char searchSpace, char value, int length)
+            => LastIndexOfValueType(ref Unsafe.As<char, short>(ref searchSpace), (short)value, length);
+
         [MethodImpl(MethodImplOptions.AggressiveInlining)]
         internal static int NonPackedIndexOfChar(ref char searchSpace, char value, int length) =>
             NonPackedIndexOfValueType<short, DontNegate<short>>(ref Unsafe.As<char, short>(ref searchSpace), (short)value, length);
@@ -1655,6 +1659,10 @@ internal static int NonPackedIndexOfValueType<TValue, TNegator>(ref TValue searc
         internal static int IndexOfAnyChar(ref char searchSpace, char value0, char value1, int length)
             => IndexOfAnyValueType(ref Unsafe.As<char, short>(ref searchSpace), (short)value0, (short)value1, length);
 
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        internal static int LastIndexOfAnyChar(ref char searchSpace, char value0, char value1, int length)
+            => LastIndexOfAnyValueType(ref Unsafe.As<char, short>(ref searchSpace), (short)value0, (short)value1, length);
+
         [MethodImpl(MethodImplOptions.AggressiveInlining)]
         internal static int IndexOfAnyValueType<T>(ref T searchSpace, T value0, T value1, int length) where T : struct, INumber<T>
             => IndexOfAnyValueType<T, DontNegate<T>>(ref searchSpace, value0, value1, length);