jquery.accessKeyLabel: Replace hardcoded brackets and space

Since If914e26f2af23f04c46f011ad8a276a9d3190583 the brackets of the
accesskey are localized, so do it also on the client side.

Also added a comment to match php and js.
Adjust tests to work on wikis with changed messages.

Bug: 65010
Change-Id: Id9908b9efcb923f0b740e2c8fd77d1ef676b489f
Merge "jquery.accessKeyLabel: Replace hardcoded brackets and space"