Fix issues with theming of preloaded ColorStateLists

Ensures changing configurations mask is propagated to the host drawable
so that it can be properly cleared from cache on configuration changes.
Also fixes constant state handling of the mask in the Inset and Rotate
drawables.

Hides new ColorStateList methods related to theming, since they should
only be used during preloading or internally by framework drawables.

Fixes bug where the cached versions of themeable ColorStateLists were
modified by calling applyTheme() on the host drawable.

Also cleans up some docs and naming in GradientDrawable.

Bug: 19966397
Change-Id: I8c8d3cabbaf94b488c2b8fe9fd423e07d824c19c