Improvements to the Inline Editor Tests

This commit basically joins all the `htmlToCSSProvider` tests inside the Inline Editor Tests into the same window. These are lots of tests where each used a single window, so this makes it faster and nicer to test. There are 3 test left that check for the Inline editor priority were each use their own window since I wasn't sure how to best change those test to be handled inside the same window. But anyway the testing is a lot nicer.

This branch is based on #4581, so is best to merge that one first.