resourceloader: Undeprecate mw.Map#values

resourceloader: Undeprecate mw.Map#values

Follows-up dc0f9b3a3a, which renamed #values to #internalValues to ease
migration to ES5 Map where such object could no longer exist in
real-time as a plain object.

However ES5 Map for mw.Map is no longer on the roadmap per T146432.
The main reason for adopting ES5 was performance, which turns out
to be invalid and was merely a bug in V8 that has since been fixed.

Change this back and undeprecate it. If anything, for developer
convience and type-ahead, which is fairly wildely used.

Change-Id: Ic19641656e53068a0aa15c27f172d39eb13620dd