Promote WP_HTTP::parse_url() to a top-level wp_parse_url function

[dd32]

WP_HTTP::parse_url() exists due to parsing bugs in < PHP 5.4.7 around schemeless URL's and IPv6, because of it's usefulness with parsing URI's which are becoming more common, we should promote it to a top-level function.

This would be beneficial to #34202

[dd32]

In 35369:

WP_HTTP: Promote the WP_HTTP::parse_url() method to a more generic wp_parse_url() function.

Fixes #34408

[dd32]

In 35370:

Use wp_parse_url() in esc_url() to avoid parsing bugs in < PHP 5.4.7.

Props johnbillion for unit tests
See #34408
Fixes #34202