[issue33839] IDLE tooltips.py: refactor and add docstrings and tests

[Terry J. Reedy]

Terry J. Reedy <tjreedy at udel.edu> added the comment:

I am going to change calltips.py and CallTips to calltip.py and Calltip in #33907, but will not change tooltip.py there as I would expect a merge conflict.  Once the change is made elsewhere, change should be made to tooltip and test_tooltip directly.

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dependencies: +IDLE: Rename calltips and CallTips as calltip and Calltip.

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