Remove explicit isBlocked(), change permission ordering to match core

* Remove explicit isBlocked everywhere. The expensive version of
  userCan does its own block check, which respects the full behavior
  of the "Prevent this user from editing their own talk page while
  blocked" checkbox (either checked or unchecked at block time).

  Per Erik, the check in RevisionActionPermissions is no longer
  necessary.

* Change permission checking order in SubmissionHandler to match core.
  Check userCan first, then later the edit filters (AbuseFilter, etc.).

* Original patch to frontend-rewrite: I0c927530f9a0ef9f1e9f56dfbe616b5a72adbfc1

Bug: 66994
Change-Id: I0c927530f9a0ef9f1e9f56dfbe616b5a72adbfc1