update_post_meta() strict checks can cause false negatives

[mukesh27]

Follow up: #22192

add_post_meta( $post_id, 'key', 1 );
update_post_meta( $post_id, 'key', 1 );

The update should not work, because they are the same. However, the meta meta cache will have "1" as a string, and then it will strict compare it to 1 as an integer. Thus, an unnecessary update will run.

It is quite common to use integers and booleans directly into these functions. They should be smart enough to recognize that "1" == 1 == true and "0" == 0 == false, and that any numeric string is also equal to a properly cast integer.

The new changes need unit tests.

Ticket from which this was spun: #22189, saving navigation menus is slow.

cc. @flixos90 @spacedmonkey @joemcgill