[0.83.x] Backport micromatch removal and dotfile/multipart watcher fix together #2027

Could the metro-file-map changes from #2000 and #2024 be backported together to the 0.83.x release line?

Both are merged on main:

• a77924694dd4e36c0a3e595956e322033a6c2c57 removes the micromatch dependency by using explicit extension, basename and basename-prefix matching.
• 3865c007c592c4ab7357f95fa6ae9e6ac735a7d1 preserves the old suffix semantics for .env, .env.local and multipart extensions such as d.ts.

The second commit is necessary: #2024 documents the Expo environment-variable reload regression when adopting #2000 alone. Expo's corresponding port is expo/expo#51093.

The current 0.83.x branch is 2ede29bc40f46dc27ac6ca4bac7a3da0d5c152b8 (0.83.8). That release line still has the metro-file-map -> micromatch -> braces dependency chain. A backport would allow consumers that need the 0.83 API/toolchain line to adopt the change without forcing a newer Metro major/minor line.

Suggested backport validation: watcher extension inclusion/exclusion, .env, .env.local, d.ts, hidden directories, package.json, health-check prefixes, and watcher backend integration tests. Please retain the 0.83 branch's existing private watcher/Flow conventions when adapting the commits.

This request is specifically for the 0.83 release line, not another main-branch implementation. It also does not imply removal of independent Jest development dependency paths. I searched existing issues and PRs for 0.83/micromatch, 0.83/braces and backport/micromatch and did not find an existing request covering this pair.