Don't use (or need) Content (again) in ViewEntityAction

The only thing is was used for at this point was to lookup
a label.

To make this most efficient, we can put the label into
parser output and get it via an OutputPage property.

Article::view takes care of everything else, in terms
of permission checking, resolving revisions for diffs, etc.

For page view:
* 5800 ms response time, 64630824 memory usage (with this patch)
* 6679 ms response time, 64812472 memory usage (on master)

On purging my large(ish) item, using xdebug, with this patch
it appears ~200ms slower (probably due to handling language fallback
there) and slight improvement to memory usage.

The improvement to page view response time is worth it.

Bug: T78265
Bug: T77134
Change-Id: I8d3f3ccdf82b9a6556df922b09f14370597280b8
(cherry picked from commit 3e2627f7312313dea3901944c954b303f473de8e)
Merge "Don't use (or need) Content (again) in ViewEntityAction" into wmf/1.25wmf12