Language Inspector: CE / DM

This is the infrastructure for the Language Inspector prototype, defining
the dm and ce pieces of the <span lang='xx' dir='yy'> annotations. It also
sets up a visual indicator for language blocks (with informational tooltip
for the user while editing. The UI is built on top of this.

Bug: 47759
Change-Id: I239eef5124e29369ea9c5d8c0f49b2f6a61bc053
Merge "Language Inspector: CE / DM"