Enable support for threaded comments and comment reply on index page

[yoavf]

Current method is missing a reference to post ID and does not allow threaded comments and replies on index pages.

The proposed patch introduce a small change to comment-reply.js and to comment-template.php (addition of post id as a parameter to the moveform function).

Two additional function are also presented in comment-template.php: get_post_reply link() and post_reply_link().
Those replicate get_comment_reply_link() and comment_reply_link() to allow for "reply" links on the posts in index pages.

Attached a patch to both /wp-includes/comment-template.php and /wp-includes/js/comment-reply.js

(In [10169]) Enable support for threaded comments and comment reply on index page, props yoavf, fixes #8550

(In [10178]) Post reply API updates. see #8550

(In [10179]) Change default add_below. see #8550

(In [10180]) Update func name. see #8550