Add keyboard layout for Belarusian

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

Bug: none
Test: connect a keyboard to a Pixel phone. Open Google search and select
"Belarusian" keyboard layout, type with keyboard.

Signed-Off-By: Siarhei Vishniakou <svv@google.com>
Change-Id: I212d8cec8bd5affcd4b825be2fa5467c2fe8976f