Support Arabic percent sign in Arabic keyboard layout

It's currently not possible to input the Arabic percent sign
on the Arabic keyboard layout; currently we use CapsLock in order
to toggle between ASCII and Arabic numerals, so we will use the
same mechanism to input it.

Bug: 355379225
Flag: EXEMPT bugfix
Test: Flashed on device, tested layout
Change-Id: Icfbce9095e2807d6ae365749cd34f9ef20a63a37