Customize: Bump `wp_custom_css_cb` from running at `wp_head` priority 11 to...

Customize: Bump `wp_custom_css_cb` from running at `wp_head` priority 11 to 101 to ensure Custom CSS overrides other CSS.

Aligns `wp_head` action priority with Jetpack's Custom CSS.

Amends [38829].
See #35395, #38672.
Fixes #39270.

Built from https://develop.svn.wordpress.org/trunk@39616


git-svn-id: https://core.svn.wordpress.org/trunk@39556 1a063a9b-81f0-0310-95a4-ce76da25c4cd