Implement efficiently non-rectangular clips in GLFunctorDrawable

Implement non-rectangular clips by writing into the stencil
buffer using new Skia API. This CL is fixing
PathClippingTests#testWebViewClipWithCircle test, which was
failing on some devices.

Bug: 34454070
Bug: 31489986
Test: CtsUiRenderingTestCases tests passed for Skia pipeline.
Change-Id: I29d7af02e2af53943540a91393f5d7a8c4e44049