Add regression test / fix for DataLabelTool

[aaronayres35]

This PR adds a regression test and a fix for the specific error reported on #550.

550 is a bit broader in scope though and would also include #802 (and probably more) to be closed.
Note the changes here were pulled from #726 in an effort to make smaller more reviewable PRs. However, there is some interconnectedness between these PRs. This PR should not be merged first, as it will break things without the change in #802

As the issue mentions, currently the DataLabelTool is forced to assume the BasaeXYPlot way or the Base2DPlot way.
"This difference forces objects that interact with AbstractPlotRenderers to make an assumption about the behavior of the map_screen method. For example, the DataLabelTool assumes the map_screen return shape matches that of BaseXYPlot for a single point ((2,)) ... And therefore this tool throws an exception when used with a Base2DPlot"

This PR makes DataLabelTool follow the Base2DPlot way (which we are pushing as the new standard), and #802 makes BaseXYPlot do the same. On this branch, DataLabelTool will not work with a BaseXYPlot.

EDIT: I've added a failing test for use of DataLabelToolwith a BaseXYPlot. This test will pass once #802 is merged

[aaronayres35]

#802 was merged, so I merged master with this branch and now CI passes as expected.

[rahulporuri]

LGTM