Address some of things found in #633

[janboddez]

Fixes some of the things found in #633

Proposed changes:

• So, wp_update_comment() doesn't actual return a comment ID.
• So I made it so that Interactions::update_comment() takes this into account and returns the $commentdata array, but only when the update was successful.
• If the update somehow failed, Interactions::update_comment() either returns false or 'invalid' (just like before) or whatever is returned by wp_update_comment() (which can be an error, or 0, or even false). Actually, in this case, the function behaves just like it did before.
• Subsequently, in the "update handler," I replaced \get_comment( $state ) with something that I think makes a bit more sense (as mentioned, $state isn't actually a comment ID).

Other information:

• Have you written new tests for your changes, if applicable?

Testing instructions:

The way I tested this, is I created a callback in a separate mu-plugin like so:

add_action( 'activitypub_handled_update', function( $activity, $second_param, $state, $reaction ) {
	if ( $reaction instanceof \WP_Comment ) {
		wp_set_comment_status( $reaction, 'hold' );
	}
}, 99, 4 );

Thing is, and this might be another bug but I left it untouched for now, I have no clue what the second param really is.

Prior to this PR, $reaction would always be null or the comment with ID 1 (but, as mentioned, the 1 returned by wp_update_comment() isn't actually a comment ID).

With this PR, $reaction is either a comment object or null. And $state basically the result of the wp_update_comment() call, kind of like before.

Either way, this short callback addresses #633. So if this PR were merged, site admins or developers would be able to much more easily force re-approval of updated comments.

[janboddez]

So the important thing is this change attempts to take into account all the different return types of Interactions::update_comment().

And then sets $state and $reaction (which in the original code would always be null or probably-the-wrong-comment) based on that.

And it's those changes that eventually allow us to use the action hook as (I assume) was intended.

Of course one could opt to have Interactions::update_comment() return something else than the $commentdata (or one of all those other return types when something goes wrong), like either a WP_Error or WP_Comment, but I tried to stay close to the current implementation. :-)

[pfefferle]

LGTM; Thanks :)