LayoutLib: add support for unsupported drawing modifiers.

DrawFilter, Rasterizer, ColorFilter and MaskFilter
are not supported but we need to provide their
JNI counterparts anyway, to at least display warnings
when they are used.

Also improved the API to query Paint for Shaders
and PathEffects, and clean up some code by
moving asserts into the DelegateManager.

Change-Id: I8942514565d28576d5608c6373bda25d86d42ff2