Compatible with JS String Builtin proposal

[oovm]

The JS String Builtin provides a set of functions to the wasm:js-string namespace, and it is best to wit them to fit into the component model system.

1. Standardize unmanaged core module imports in the wasm:js-string namespace
2. Host can selectively implement some js functions
3. Linker can select the required shim implementation
4. As a shared core definition, other js binding libraries can import and pass js strings without loss

There are many details to discuss, such as

• wasm:js-string is not a valid world name
• Is js-string a resource?