Add tests to ensure cross-workspace reloading works ok

[airhorns]

This fixes 3 issues introduced in the ESM rewrite:

• the ESM changes meant that we accidentally stopped watching the workspace root, and only started watching the folder that the first invoked script was in. Oops! Now we climb up to the workspace root for both pnpm and yarn.
• The ignore globs support was sketchy and wasn't correctly re-using the ignore globs for both the search for files to compile and the watcher's list of files to watch. This switches us around to centralize where we build the globs and ensure we respect them as actual globs in the watcher, relative to the project root dir they came from
• The ignore glob processing was super slow, using globby to check again if a file was ignored every time! Oops, too slow! This fixes that to use an in-memory glob match to see if a file is ignored, instead of re-globbing.