External types

[skeet70]

This required small changes to uniffi to thread all the external values we needed for a fully qualified RustBuffer through. Also some big changes to our code to thread config through basically all over the place to support fully qualified external types.

This also prompted that for subdependencies we can't do the uniffi.toml extension trick we've been doing in the tests (see custom_types usage in TestImportedTypes. I wrote up a failed attempt at doing something similar in the branch failed-rewrite-uniffi-toml-dep, but the overwritten values aren't used in the build and we don't have a way to manually pass the overrides down to subdependencies like we are for the top level fixtures with our generate_bindings call. For now I just changed the tests to not expect the nice URL swapping to work, but long term hopefully there's a better way.

[github-actions]

File	Coverage	Lines
All files	79%	79%	✅
src/gen_java/enum_.rs	50%	50%	✅
src/gen_java/primitives.rs	20%	20%	✅
src/gen_java/variant.rs	50%	50%	✅
src/gen_java/compounds.rs	78%	78%	✅
src/gen_java/mod.rs	89%	89%	✅

Minimum allowed coverage is 0%

Generated by 🐒 cobertura-action against 50a1534

[coltfred]

Looks like the test failure is the flaky multi-threading test from CI?

I think this all looks good. Threading the config everywhere is kind of 😢, but I don't see a better way.