[3.13] gh-143774 - Improve IDLE Format Paragraph doc (GH-143775) (#144063)

gh-143774 - Improve IDLE Format Paragraph doc (GH-143775)

Add a reminder to not rewrap code line to the Menu => Format => Reformat Paragraph entry.
In Editing and Nagivagion, add a new 'Format block' subsection that defines 'paragraph'
to better match what is dependably handled as more or less expected.
In particular, specify equal indents and that the resulting indent equals original indent.
Also mention that selections are expanded to complete lines and how to modify max length.

(Also fix a couple case errors in cross references.)
(cherry picked from commit fa3abf5a51d42b2d62e1bc89e9465b398a567e94)

Co-authored-by: Terry Jan Reedy <tjreedy@udel.edu>