ParserOutput: Add 'deduplicateStyles' post-cache transformation

ParserOutput: Add 'deduplicateStyles' post-cache transformation

This transformation will find <style> tag with a "data-mw-deduplicate"
attribute. For each value of the attribute, the first instance will be
kept as-is, while any subsequent tags with the same value will be
replaced by a <link rel="mw-deduplicated-inline-style"> with its href
referring to the "data-mw-deduplicate" value using a custom scheme.

This also adds an $attribs parameter to Html::inlineStyle() so the
data-mw-deduplicate attribute can be added.

Note this doesn't actually depend on Ib931e25c, but action=mobileview
will break if it starts being used without that patch.

Bug: T160563
Change-Id: I055abdf4d73ec65771eaa4fe0999ec907c831568
Depends-On: Ib931e25ce85072000e62c486bbe5907f03372494