amend! ci(primitives): transition to new css primitives

ci(primitives): transition to new css primitives

GitHub no longer distributes primitives in JSON format. Also, the names
of the values (i.e. CSS variables) have changed. Most of the new names
correspond 1-to-1 with one of the old names. Some colors have also
changed slightly (e.g. `fg-default`), but otherwise remain mostly the
same. See https://primer.style/foundations/primitives/migrating.

Source color primitives from `@primer/primitives/dist/internalCss`
instead of `@primer/primitives/dist/css/functional/themes` as only the
former directory contains the base colors (scales).

Convert new primer css primitives/variables directly to lua in
.github/workflows/csstolua.lua (runs in CI). This script generates some
debugging info in case an error occurs (which can be found in CI logs).
Convert to a nested table structure for idiomatic usage in lua. The
primitives table now provides type-hints via lsp, and accessing invalid
names at runtime will throw an error. Append `.default` to
names/keypaths which are too short and would otherwise collide with
existing tables.

- `scale` no longer exists, but is still provided (by us) for
  backwards-compatibility and ergonomics. The new names are in the
  format of `base.color.red[4]` (for example to access `scale.red[5]`).
  The values in `scale` are 1-indexed for lua, but the original upstream
  names (in `base.color.*`) are 0-indexed and left untouched.

- `scale.gray` no longer exists, use `scale.neutral` in its place

- `*.subtle` variants no longer exist, see the link above for the
  corresponding replacements