[3.12] gh-129699: Add description to IDLE doc title (GH-129727) (#129865)

gh-129699: Add description to IDLE doc title (GH-129727)

Also extend the 'idlelib' section header. These additions affect both the displayed idle.html file and the contents.html file displayed by clicking the Complete table of contents link on the main docs.python.org page. (The module index entries are generated from the module name and synopsis within module files.)
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(cherry picked from commit 33a7094aa680bca66582fec4dcda7d150eb90cd8)

Co-authored-by: Stan Ulbrych <89152624+StanFromIreland@users.noreply.github.com>
Co-authored-by: Terry Jan Reedy <tjreedy@udel.edu>