Fix #14313: Optimize jQuery.merge for size. Close gh-1344.
Ref #14313: Further code and test improvements
No ticket: Hide the testing-support jQuery from tests
Merge remote-tracking branch 'upstream/master' into grep-test

* upstream/master:
  No ticket: Hide the testing-support jQuery from tests
  Ref #14313: Further code and test improvements
  Fix #14313: Optimize jQuery.merge for size. Close gh-1344.