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.

Built from https://develop.svn.wordpress.org/trunk@26906


git-svn-id: http://core.svn.wordpress.org/trunk@26789 1a063a9b-81f0-0310-95a4-ce76da25c4cd