Possible incorrect type for $comment_id in get_comment_author filter

[david.binda]

After r52818 the $comment_id param of the get_comment_author filter, which is documented as numeric string, may be an int, in case a non-existing comment ID is passed to the get_comment_author function.

The topic has been briefly discussed in https://core.trac.wordpress.org/ticket/54379#comment:8 mentioning that the numeric string type is here for compatibility.

I'm attaching a patch containing a fix for the issue, as well as a PHPUnit test demonstrating the behaviour.

[SergeyBiryukov]

In 58335:

Comments: Ensure the correct comment ID type is passed to get_comment_author.

The $comment_id parameter of the get_comment_author filter is documented as a numeric string, however in case a non-existing comment ID is passed to the get_comment_author() function, it could be an integer instead.

This commit resolves the issue and adds a PHPUnit test demonstrating the behavior.

Includes updating get_comment_author_url() unit tests for consistency.

Follow-up to [41127], [52818].

Props david.binda.
Fixes #60475.