Inline documentation improvements for get_*_template() functions in wp-includes/template.php.

* Adds `@see` references for `get_query_template()` or similar
* Adds complete `@return` descriptions
* Clarifies which dynamic hooks can be used to filter specific template types

Props UmeshSingla for the initial patches. Props SergeyBiryukov, DrewAPicture.
Fixes #26742.


git-svn-id: https://develop.svn.wordpress.org/trunk@26906 602fd350-edb4-49c9-b593-d223f7449a82