resourceloader: Un-deprecate ClientHtml::setModuleStyles()

resourceloader: Un-deprecate ClientHtml::setModuleStyles()

This follows 80e5b160e0985, which introduced ClientHtml::setModuleScripts()
and setModuleStyles() with @deprecated marks. There was a vague intention
to remove both at some point.

The commit did not deprecate the related methods in OutputPage and ParserOutput.

The plan that eventually formed at T188689 was to keep methods relating to
"setModuleStyles" for the time being, and focus first on the removal of the
methods relating to "setModuleScripts". The latter since been properly
marked as deprecated and removal is scheduled for 1.33.

There is no current plan to deprecate/remove addModuleStyles
from OutputPage and ParserOutput. As such, the internal helper method
that makes those possible, probably shouldn't me marked as deprecated.

Bug: T188689
Change-Id: Ia36c057b73fe834bcbb2e3e8993d1a793a12ab72