Add Mongolian keyboard layout support

Add keyboard layout support for entering Mongolian text. This will be used
for connecting a physical keyboard and typing in Mongolian.

Bug: 141126644
Test: connect USB/Bluetooth keyboard and choose "Mongolian" keyboard
layout, start typing in a input window.

Change-Id: Ie18a915199d47b6ba58b11eafaaab9a1f6f2f470
Merged-In: Ie18a915199d47b6ba58b11eafaaab9a1f6f2f470