AD. Issue 62760. Optimize LibraryContext.remove

Update library invalidation so `LibraryContext.remove()` can identify
removed library cycles directly from the removed files.

Previously file eviction cleared `file._kind` before
`LibraryContext.remove()` ran. Once that happened, the library cycle for
a removed file was no longer available, so removal had to scan all
loaded bundles and check whether any cycle contained one of the removed
files.

Run bundle removal while file kinds are still intact and have
`LibraryContext.remove()` derive the affected cycles directly from the
removed files. This lets it remove those cycles from `loadedBundles` and
collect their linked keys without scanning unrelated bundles.

To support this ordering, file-state pruning now exposes a hook that
runs before disposal begins, and file change handling collects affected
files before evicting them. This keeps library invalidation targeted and
avoids extra work during cache cleanup.

Bug: https://github.com/dart-lang/sdk/issues/62760
Change-Id: I5055606eead4dce2f65a0fcaf52acf0d53a93c61
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/487701
Reviewed-by: Johnni Winther <johnniwinther@google.com>
Commit-Queue: Konstantin Shcheglov <scheglov@google.com>