Unit tests hang after CodeMirror patches for issue #1787

[jasonsanjose]

Spun off from #4564.

@RaymondLim reported that unit tests hang after doing a local merge for cursor positioning fixes in codemirror/codemirror5#1787 (comment)

These fixes have not landed in Brackets yet, but we do integrate CodeMirror upstream/master at the beginning of every sprint. This will be an issue at the start of Sprint 32.

[njx]

The hang appears to be during createMockEditor(). Probably something to do with the fact that we create a fake editor holder.

[njx]

Looks like the problem is just that our unit tests create mock editors inside an element that has no explicit width (and is absolutely positioned, so has no inherent width). That didn't cause a problem before, but it's understandable why Marijn's change would have broken this. It's arguably a CM bug, but since this isn't a realistic use case I think we can just change our unit tests to set an explicit width on the mock editor holder.

[njx]

Fixed this while merging the latest CM. Closing.