[dart2wasm] Add missing polyfill for wasm:js-string.test and remove unused (and not polyfilled) wasm:js-string.fromCodePoint

This is a follow up to [0] that started to make use of
`wasm:js-string.test`.

[0] https://dart-review.googlesource.com/c/sdk/+/429362

Closes #60763

Change-Id: Iac4b6ad1b845a486e4b8583e18d5f0941f55add6
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/429943
Commit-Queue: Martin Kustermann <[email protected]>
Reviewed-by: Ömer Ağacan <[email protected]>

Author: mkustermann

pkg/dart2wasm/lib/js/runtime_blob.dart

@@ -173,6 +173,7 @@ const jsStringPolyfill = {
         }
         return s.length;
       },
+      "test": (s) => typeof s == "string",
     };
 ''';
 

sdk/lib/_internal/wasm/lib/js_string.dart

@@ -999,9 +999,6 @@ external WasmI32 _jsStringEqualsImport(WasmExternRef? s1, WasmExternRef? s2);
 @pragma("wasm:import", "wasm:js-string.fromCharCode")
 external WasmExternRef _jsStringFromCharCodeImport(WasmI32 c);
 
-@pragma("wasm:import", "wasm:js-string.fromCodePoint")
-external WasmExternRef _jsStringFromCodePointImport(WasmI32 c);
-
 @pragma("wasm:import", "wasm:js-string.length")
 external WasmI32 _jsStringLengthImport(WasmExternRef? s);