gh-92822: IDLE - Add a selection label to window statusbars

[tomlin7]

When a selection is made, add a selection label after cursor row/column labels.
While a selection is present, update it on <<set-line-and-column event>>.

• Issue: IDLE: Add "selected" section to Statusbar #92822

[cpython-cla-bot]

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[bedevere-bot]

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[terryjreedy]

I have not yet accepted the addition, let alone the format; further edits should await approval of both. See issue.

If accepted, new tests will be needed. Running tests before they are added is useless.

[terryjreedy]

Suggested change applies regardless of possible format change.

[bedevere-bot]

A Python core developer has requested some changes be made to your pull request before we can consider merging it. If you could please address their requests along with any other requests in other reviews from core developers that would be appreciated.

Once you have made the requested changes, please leave a comment on this pull request containing the phrase I have made the requested changes; please review again. I will then notify any core developers who have left a review that you're ready for them to take another look at this pull request.

[tomlin7]

@terryjreedy I have made the requested changes; please review again

[bedevere-bot]

Thanks for making the requested changes!

@terryjreedy: please review the changes made to this pull request.