#7422 may have regressed - click on the top pixel of a tab when maximized

From discussion on a0670cb6b3e57dde525af1a04563e94ce80b5390

> Interestingly, the compensation for GH #10746 might have caused 10746 to stop functioning by pushing the application body down one more pixel. I can't get the tab bar hit targets at the top of the screen when maximized to work any longer.

> @DHowett If you've got a repro for that, can you fix that again? I checked out this PR when it was first opened to make sure that one was still fixed, but I guess I didn't have my monitors in the very peculiar config that repro'd #7422 in the first place.

This might also be the #11294 issue, but unlikely Dustin had the MUX commit at the time.

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This also applies to the new tab dropdown combo button.

Start with the discussion at commit a0670cb6b3e57dde525af1a04563e94ce80b5390 and compare issues #7422, #10746, and #11294. Reproduce the problem with the application maximized, then verify that the top-pixel tab targets and the new-tab dropdown combo button respond correctly.

Written by the indexing model from the issue text.