Make PR merge options more intuitive (#5863) (#16582)

Reword options making clear whether the PRed branch is rebased or not, and which type of commit will be created if any.

Author: aaribaud

options/locale/locale_en-US.ini

@@ -1437,10 +1437,10 @@ pulls.no_merge_helper = Enable merge options in the repository settings or merge
 pulls.no_merge_wip = This pull request can not be merged because it is marked as being a work in progress.
 pulls.no_merge_not_ready = This pull request is not ready to be merged, check review status and status checks.
 pulls.no_merge_access = You are not authorized to merge this pull request.
-pulls.merge_pull_request = Merge Pull Request
-pulls.rebase_merge_pull_request = Rebase and Merge
-pulls.rebase_merge_commit_pull_request = Rebase and Merge (--no-ff)
-pulls.squash_merge_pull_request = Squash and Merge
+pulls.merge_pull_request = Create merge commit
+pulls.rebase_merge_pull_request = Rebase then fast-forward
+pulls.rebase_merge_commit_pull_request = Rebase then create merge commit
+pulls.squash_merge_pull_request = Create squash commit
 pulls.merge_manually = Manually merged
 pulls.merge_commit_id = The merge commit ID
 pulls.require_signed_wont_sign = The branch requires signed commits but this merge will not be signed