Create get_author_posts_link() function to return rather than echo HTML-formatted author posts link

[chipbennett]

Patch is fairly simple:

1. Create get_author_posts_link() function, which is identical to current the_author_posts_link() function, except that the output is *returned* instead of *echoed*.
2. Change the_author_posts_link() to echo the output of get_author_posts_link().

The primary purpose for creating the patch is to allow for the return value to be used in translation strings via sprintf(). Though, I'm sure there will be other uses.

[obenland]

I like it, sounds like a sound improvement.

A few things I noticed:

• We should probably call it get_the_author_posts_link().
• The comment for the_author_posts_link() can start with "Display" again, rather than "Get".
• the_author_posts_link() would need to continue accepting the deprecated argument.
• We can drop the deprecated argument from get_the_author_posts_link() and don't need to pass it to it in the display function.
• The double line break between the two functions should probably just remain one.
• I'm not sure we need to update the function body with current coding guidelines, since it doesn't really need alterations, except for returning the result.

[zrothauser]

Updated functions

[chipbennett]

Thanks, @zrothauser, you beat me to it.

[wonderboymusic]

Refreshed so it doesn't explode 30355.2.diff​

[DrewAPicture]

In 34677:

Introduce get_the_author_posts_link(), which returns the HTML link to the author page for the current post's author.

the_author_posts_link() has in-turn been converted into a wrapper, with most of its logic moved to the new function.

Adds tests for the new function.

Props chipbennett, zrothauser, wonderboymusic, DrewAPicture.
Fixes #30355.

[DrewAPicture]

In 34678:

Tests: Flush rewrite rules between tests in an attempt to avoid permalinks pollution in Tests_Author_Template.

See #30355.