This change introduces the following features to Keyboard XML format.
* "keyXPos" can specify the key X coordinate directly.
* "keyXPos" can be negative. The X coordinate will be calcluated from
the right edge of the keyboard toward left.
* "keyWidth" can be zero to be filled up to the right side.
* "keyWidth can be negative. The key will be filled up to both sides.
* Spacer's horizontalGap is renamed as keyWidth, and can be inherited
from key-style.
* Spacer can have keyXPos attribute.
Using these syntax, all keyboard layouts have been re-written.
Cherry-Pick: I314b2e8ca2aa145ff9506cbf927140a15685af42
Bug: 4442045
Change-Id: I048fe5eaef020d8472ab577e9d326042bae2f3fa
