Update .wit files to allow referencing between host and guest interfaces

[Forthoney]

Currently, we use JsValueTransport to facilitate moving values between the rb-abi-host and rb-abi-guest. Since the introduction of this workaround in #18 (May 2022), the WIT format implemented features such as worlds and import/exports. If we update our .wit files to use these new features I think JsValueTransport would no longer needed because the host and guest .wit can reference each other.

[Forthoney]

My proposal is to

1. Created a single wit directory where we store both .wit files as suggested by the WIT docs
2. Wrap each file's current content inside an interface
3. Use a use statement to reference js-abi-value in guest and rb-abi-value host

This may need a good bit of reorganizing of the current project structure. I'm frankly unsure what implications moving files around will have (especially in regards to C files currently in the same directory as the .wit files). I would appreciate some insight on this.

[kateinoigakukun]

Thank you for your proposal! Yeah, I'm positive for using the latest WIT spec's import/export to describe the hack in the right way. It looks like wit-bindgen now supports resource feature in C. Also we can use jco to import the component from JS host side.