Detect unhandled keyboard focused state.

A View uses a Drawable as its background, which changes
its appearance according to the View's state. This commit
adds an algorithm to detect undefined state_focused in
state specs for those Drawables.

Test: cts-tradefed run singleCommand cts --skip-device-info
--skip-preconditions --abi armeabi-v7a -m CtsGraphicsTestCases
-t android.graphics.drawable.cts.DefaultFocusHighlightTest
Bug: 35096940

Change-Id: I5e9f07141679881fe88f9040aa116ea2f9d537c9