Split up ext.visualEditor.mwcore into smaller parts

Core retains core functionality, including text styling and architectural
items like dialogs.

The new modules are:
* mwformatting
* mwimage
* mwlink
* mwmeta
* mwreference
* mwtransclusion

The new modules are loaded in ViewPageTarget (for desktop), except for
mwlinks which is included from MWTarget (for desktop and mobile), per the
needs of the Mobile team.

Also, mwgallery was moved to desktop-only loading status.

Some styles which were loaded in mwcore but only used in modules is now
loaded in said modules.

This does not split up ext.visualEditor.core yet, which is left as an
exercise for the fool-hardy.

Bug: 61075
Change-Id: I6374854eaa13af824c11078d2f7004dc8a211a30
Merge "Split up ext.visualEditor.mwcore into smaller parts"