Switch to pnpm

[NullVoxPopuli]

yarn@v1 can't be trusted. this has been known for ages.
Also, newer tooling isn't supporting yarn@v1.

unblocks: #668

Changes:

• remove yarn
• add pnpm
• Support isolated packages
  (a requirement to get types passing)
  Previously, everything was all loosey goosey / incorrect.
  • @glimmer/runtime was not specified, adding it adds the ESM version of Glimmer. No modern version of @glimmer/* exports CJS, and thus is not compatible with Glint (which is compiled to CJS (because VSCode extensions don't support ESM))
  • @glint/core was added to any package that invokes the glint bin. This is required, because bin directories are are local to each package.
  • Other glint packages were added to each package that imports from them, because there is no more hoisting, which means TS can't find the packages unless they are declared in the package.json. This has been done as devDependencies
  • We can't have dependencies loosely importing from all over the place, so extra packages have been extracted for integration testing
    • Example: @glint/core cannot have tests that consume any environment package, because the environment packages depend on @glint/core
  • There are resolution issues with the environments. :(

[NullVoxPopuli]

we can't import from Glimmer, because Glimmer is ESM, and Glint is not.

[NullVoxPopuli]

Alternatively, the tests could be extracted to an ESM package, but then we'd lose the ability to test private things.

A solution could be vitest's in-source testing.
This would require revamping how all the glint packages are built though. (not using tsc)