Improve IDLE Format Paragraph doc

[terryjreedy]

Improve the IDLE doc entry for the Format / Format Paragraph menu item, based on this discuss topic.

• Define 'paragraph' to better match what is dependably handled as more or less expected. In particular, specify equal indents.
• Mention that indent of result is indent of paragraph.
• And how to modify max length.
• And to not rewrap code.

I consider the last point to be implicit in the current entry and more obviously so in the revision already prepared. I included it in the initial version but will consider removing it after more discussion.

Linked PRs

• gh-143774 - Improve IDLE Format Paragraph doc #143775