[analysis_server] Move CodeActionKind filter earlier in production of code actions

This removes a filter of CodeActionKinds from the final step (and a class named `_CodeActionSorter`!) and instead applies it earlier during building of the actions. This will help apply the filter in the case where we return bare Commands (which don't have `kind`s) instead of `CodeActionLiteral`s.

I added some TODOs because I still don't think this is filtering early enough (because in the case of invoking an action via the command, we need to not have to produce _all_ code actions just to locate the _one_ we want to execute), but it's a step closer (and easier to review this without it being lumped in with the CL that supports returning Commands).

Change-Id: Ibc73c4900d939ac833f6345e9e8f1fdf3f5d6823
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/427000
Reviewed-by: Samuel Rawlins <srawlins@google.com>
Reviewed-by: Brian Wilkerson <brianwilkerson@google.com>
Commit-Queue: Brian Wilkerson <brianwilkerson@google.com>