String.charCodeAt should return int (#7864)

* String.charCodeAt should return int

* CHANGELOG

Author: cknitt

CHANGELOG.md

@@ -14,6 +14,8 @@
 
 #### :boom: Breaking Change
 
+- Fix return type of `String.charCodeAt`. https://github.com/rescript-lang/rescript/pull/7864
+
 #### :eyeglasses: Spec Compliance
 
 #### :rocket: New Feature

packages/@rescript/runtime/Stdlib_String.res

@@ -17,7 +17,7 @@ external compare: (string, string) => Stdlib_Ordering.t = "%compare"
 @get_index external getUnsafe: (string, int) => string = ""
 @send external charAt: (string, int) => string = "charAt"
 
-@send external charCodeAt: (string, int) => float = "charCodeAt"
+@send external charCodeAt: (string, int) => int = "charCodeAt"
 @send external codePointAt: (string, int) => option<int> = "codePointAt"
 
 @send external concat: (string, string) => string = "concat"

packages/@rescript/runtime/Stdlib_String.resi

@@ -220,12 +220,12 @@ See [`String.charCodeAt`](https://developer.mozilla.org/en-US/docs/Web/JavaScrip
 ## Examples
 
 ```rescript
-String.charCodeAt(`😺`, 0) == 0xd83d->Int.toFloat
+String.charCodeAt(`😺`, 0) == 0xd83d
 String.codePointAt(`😺`, 0) == Some(0x1f63a)
 ```
 */
 @send
-external charCodeAt: (string, int) => float = "charCodeAt"
+external charCodeAt: (string, int) => int = "charCodeAt"
 
 /**
 `codePointAt(str, index)` returns the code point at position `index` within