4.1 Docs Audit: Improve inline documentation for various properties and methods in the `WP_Customize_Section`, `WP_Customize_Section`, and `WP_Customize_Sidebar_Section` classes.

See #30469.


git-svn-id: https://develop.svn.wordpress.org/trunk@30608 602fd350-edb4-49c9-b593-d223f7449a82