Use API internally for post/page/media edit links

[mdawaffe]

Plugins adding new types of post types or adding specific functionality for specific media mime types may need more flexibility than simply adding form fields to a post's, page's or media item's edit screen. These plugins may need to offer completely new edit screens for their specialized data.

WordPress currently has post, page, and media item edit links hardcoded rather than using the filterable get_edit_post_link() function.

The attached converts all the hardcoded links to links created with get_edit_post_link().

[ryan]

(In [8484]) Use get_edit_post_link() instead of hardcoding edit links. Props mdawaffe. fixes #7425