Resolve styles by font table if not specified.

android:fontStyle and android:fontWeight is an optional attribute.
If they are missing, we are using non-italic 400 weight, but this is
not good idea. We should resolve these style value from font metadata.

Bug: 37988154
Test: am instrument -w -e class android.content.res.cts.ResourcesTest
      android.content.cts/android.support.test.runner.AndroidJUnitRunner

Change-Id: I80a436cd3632d8c58fa3d8bdaedac73b95f61a8c