Work around T87871 to avoid double-loading OOjs UI PHP styles

Work around T87871 to avoid double-loading OOjs UI PHP styles

Use a <meta> tag added when enabling OOUI, and a skipFunction that
looks for it, to avoid double-loading the modules: oojs-ui.styles,
oojs-ui.styles.icons, oojs-ui.styles.indicators, oojs-ui.styles.textures.

This saves us loading of around 200K of CSS (20K when gzipped) on pages
that both use OOjs UI PHP server-side and load OOjs UI client-side.
(For example, all MediaWiki special pages using OOUIHTMLForm.)

Interesting caveat: this causes the aforementioned modules to no
longer appear in the output of `mw.loader.inspect()` on such pages.

Bug: T125292
Change-Id: Ia7e2256cd239841e1f78c4a6bf666dd939c0d2c7