refactor: minor cleanups in webpack actions code (#75912)
this is a bundle of small cleanups i did while working on
https://github.com/vercel/next.js/pull/75908, and i decided to pull them
out.
**this PR is intended to be reviewed commit-by-commit**.
i don't want to turn this into a stack because that'll take much longer
to merge (unless someone REALLY wants me to)
changes by commit:
1. i removed `RSCMeta.actions`, because it was unused except for one
place where `RSCMeta.actionIds` is enough
2. fixed some places that were accessing `module.buildInfo.rsc` in a
non-typesafe way, removed redundant `getActionsFromBuildInfo` helper
3. added some type safety to the huge queryparam passed to
`next-flight-action-entry-loader`
4. replaced some `[id, name]` tuples in `flight-client-entry-plugin`
`next-flight-action-entry-loader` with `{ id, exportedName }`. IMHO
tuples where both items are the same type are asking for trouble, names
are harder to mess up
