Problem: The 3rd-party default homebrew tap `aws/tap` is untrusted,
which now triggers a warning in our macOS workflows.

Solution: "Untap" (disable) the tap (which we don't use).

Problem: Support for Intel macOS is increasingly being dropped since
Apple itself retired the architecture (with macOS 27 already being
ARM-only). In particular, homebrew is already dropping support, with
some 3rd-party taps like `hashicorp/tap/vagrant` (that are enabled on GH
runners by default) no longer being available. This makes `brew upgrade`
fail on Intel.

Solution: Skip `brew upgrade` in `install_deps.sh`, as we don't rely on
the bleeding edge version of the installed dependencies. This skips
checking the tap (which we don't use) and hence lets the workflows pass.
(It also shaves of some seconds from the CI time.)

Note: This is strictly speaking a GHA issue and should be handled by
adapting the runner images; but since GHA has already announced that
they will drop all Intel macOS images in 2027, this is unlikely to
happen.

It also means that this is a stopgap solution to allow 0.13 to keep Tier
1 support for Intel macOS, but next year we'll have to drop support as
well.

Add a dedicated nvim.wasm build workflow and
include the resulting WASM artifact in nightly releases.

Problem:
- The `reviewers_add`/`reviewers_remove` CI jobs checkout the repo only
  for the purpose of `require('…/reviewers_add.js')`.
- `reviewers_remove` also runs on `closed`, so a merged fork PR will trip
  the new allow-unsafe-pr-checkout guard of `actions/checkout@v7`.

Solution:
- Drop the use of `actions/checkout`.
- Inline the script in the CI yaml definitions.
- Also await the mutating calls (previously fire-and-forget) and guard
  empty reviewer lists.

- `src/nvim/ex_cmds_defs.h`: use "U" instead of "u" per
  `readability-uppercase-literal-suffix`

docs: lsp, options

- revert bogus change to `_meta/builtin_types.lua` from 3a4a66017b74

Close #38991

Co-authored-by: David Mejorado <david.mejorado@gmail.com>