Fix flag for js string builtins (#411)

Run 
```bash
deno --v8-flags=--help
node --help --v8-options
```

And there's no `experimental-wasm-js-string-builtins`. Instead, it's `
--experimental-wasm-imported-strings`

features.json

@@ -250,7 +250,7 @@
 				"gc": "22.0",
 				"instrumentAndTracingTechnology": ["flag", "Requires flag `--experimental-wasm-instruction-tracing`"],
 				"jspi": ["flag", "Requires flag `--experimental-wasm-jspi`"],
-				"jsStringBuiltins": ["flag", "Requires flag `--experimental-wasm-js-string-builtins`"],
+				"jsStringBuiltins": ["flag", "Requires flag `--experimental-wasm-imported-strings`"],
 				"memory64": ["flag", "Requires flag `--experimental-wasm-memory64`"],
 				"multiMemory": "22.0",
 				"multiValue": "15.0",
@@ -282,7 +282,7 @@
 				"gc": "1.38",
 				"instrumentAndTracingTechnology": ["flag", "Requires flag `--v8-flags=--experimental-wasm-instruction-tracing`"],
 				"jspi": ["flag", "Requires flag `--v8-flags=--experimental-wasm-jspi`"],
-				"jsStringBuiltins": ["flag", "Requires flag `--v8-flags=--experimental-wasm-js-string-builtins`"],
+				"jsStringBuiltins": ["flag", "Requires flag `--v8-flags=--experimental-wasm-imported-strings`"],
 				"memory64": ["flag", "Requires flag `--v8-flags=--experimental-wasm-memory64`"],
 				"multiMemory": "1.38",
 				"multiValue": "1.3.2",