Previously, the `isCommitClosingPullRequest()` method (used in
`ng-dev release` to detect whether a commit is closing a PR based on
keywords found in the commit message) was only able to detect a subset
of the keywords supported by GitHub.
This is fine currently, because the merge script adds `PR Close #XYZ`
when merging a PR, but it might break in the future.
This commit makes the code more robust by ensuring the method can detect
all keywords supported by GitHub for automatically closing a PR based on
a commit message.
Original discussion:
https://github.com/angular/angular/pull/39135#discussion_r503440973
PR Close#39229
96dd78e0c6