Improve inline documentation for `image_constrain_size_for_editor()`.

Includes:
* Proper formatting, plus adding a type for the `$context` parameter
* Inline `@see` tags in the description and backtick-escaping inline code
* Parameter, type, and description alignment

Props tillkruess for the initial patch.
Fixes #30508.


git-svn-id: https://develop.svn.wordpress.org/trunk@30646 602fd350-edb4-49c9-b593-d223f7449a82