Implement drop and inner shadow styles using explicit image filters.
Remove existing style support from DropShadowEffect.cpp, as it now
has a new cozy place with its inner sibling.
Supported properties:
- color
- opacity
- angle
- distance
- size (sigma)
Change-Id: I5b7e3c75678e036a20c1908b84c74a670a5aa196
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/283918
Reviewed-by: Michael Ludwig <michaelludwig@google.com>
Commit-Queue: Florin Malita <fmalita@chromium.org>
