Coverall2 and Rondpoint working with WASM!

[jhugman]

This PR adds:

• lowlevel structures
  • RustBuffers,
  • Floats and
  • c_void Void Pointers.
• high level mechanisms to do in a browser context:
  • encoding and decoding strings, using TextEncoder and TextDecoder.
  • tie Objects into the Garbage Collector with a FinalizationRegistry.

This is in service of getting the rondpoint fixture running.

Several things to note here:

error: rondpointpm::Optionneur is a private type

Structs which derive the uniffi::Object currently need to have visibility pub. If they're not, then errors like: error: rondpointpm::Optionneur is a private type are shown.

This is due to uniffi-rs generating a public C ABI which uses the private struct as part of its trait bounds. This feels like it's a Rust bug (I hate saying that).

Next steps:

• File an issue:
  • uniffi-rs could generate a simpler ABI which didn't contain the private type.
  • uniffi-rs could prevent non-pub structs
• Document: uniffi-bindgen-react-native should add this to a trouble-shooting page.

Additing a procmacro version of rondpoint and coverall2

This is due to mozilla/uniffi-rs#2329 not yet being release.

Since we have now released to CocoaPods and npm, I can build against uniffi-main. This is o k a y for a little project like this, but I do worry about that a chem-spill requiring a rapid fix and release may get messy.

Default attribute values not seeming to work in proc-macro uniffi::Record

I don't seem to be able to get default attributes working for records going: as in the typescript isn't getting generated. If this is a bug, this is almost certainly a uniffi-rs bug. Will file.