Problem:
The magic globals `it`, `describe`, etc., are more trouble than they are
worth.
- Hooking into `after_each` requires `getfenv()` hacks.
- They confuse luals/emmylua, because the top-level `.luarc.json` isn't
merged with `test/.luarc.json` (apparently a luals limitation?)
- They totally defeat discoverability because the user just has to
"know" about the various magic symbols.
So they harm DX, which means they serve no purpose at all.
Solution:
- Expose the test API from `testutil`, so tests can call `t.it()`,
`t.describe()`, etc., in the conventional way.
- Drop `getfenv()` hacks.
- Drop the `setfenv()` injection in `load_chunk`.
- Drop `test/_meta.lua`.
Problem:
`test/functional/plugin/lsp_spec.lua` had grown into a large catch-all file that mixed core LSP client lifecycle coverage, `vim.lsp.buf.*` behavior, and `vim.lsp.util.*` behavior in one place.
Solution:
Split the large tests into more focused test files without changing test coverage or intended behavior.
After this change, `lsp_spec.lua` is more focused on core LSP client/config/dynamic-registration behavior.
