Do not support JS strings beyond 2^32 bytes

Author: daxpedda

proposals/js-text-encoding-builtins/Overview.md

@@ -168,7 +168,7 @@ func encodeStringIntoUTF8Memory(
   string: externref,
   start: i64,
   end: i64
-) -> (i64, i64)
+) -> (i32, i64)
 {
   start >>>= 0;
   end >>>= 0;
@@ -213,3 +213,7 @@ The JS String Builtins proposal already exposes [`"wasm:js-string" "substring"`]
 ### `"wasm:text-encoding"` vs `"wasm:js/text-encoding"`.
 
 There is an [ongoing discussion](https://github.com/WebAssembly/esm-integration/issues/118) to change the mapping for JS builtins. Either convention works for us in this proposal.
+
+### What about JS strings larger than 2^32 bytes?
+
+Given that currently no engine supports strings larger than 2^30 and there are currently no plans to do so, we concluded to postpone specifically addressing this. See [#3](https://github.com/WebAssembly/js-text-encoding-builtins/issues/3).