ve.init.mw.ViewPageTarget: Switch tabLayout from 'add' to 'replace'

This makes the Edit tab point to the VisualEditor, and adds a
"Edit source" link to the p-cactions menu.

Bug: 46872
Change-Id: I559232f3d8e42df0d45311b65df8c30425b1a368
ve.init.mw.ViewPageTarget: Put the Edit source link in the visible tab area

Instead of in the collapsed section.

Change-Id: I7b0e3fa4e35ce6135e3a47360da51fd8e0231ca1
Merge changes I7b0e3fa4,I559232f3

* changes:
  ve.init.mw.ViewPageTarget: Put the Edit source link in the visible tab area
  ve.init.mw.ViewPageTarget: Switch tabLayout from 'add' to 'replace'