Improve CanvasState cross-library tests

Several things are accomplished as part of this:
1. The canvas_state_lib build target is brought back so that we can
   actually test the canvas state sharing across library boundaries.
2. The canvas state helper functions are updated to work with DLLs
   (confirmed tests pass on Windows in cross library mode)
3. The tests now always run, and the cross-state define only changes
   what version of the helper functions are used
4. Updated the dlopen code in the test to use the SkOSLibrary ports
   instead of calling dlopen/dlclose directly.
5. Fix bugs in SkCanvasStateUtils that were uncovered as part of
   always running these tests.
6. Switches the define away from SK_SUPPORT_LEGACY_CLIPTOLAYERFLAG
   to SK_TEST_CANVAS_STATE_CROSS_LIBRARY, since these tests are not
   strictly speaking testing the unclipped layer feature.

Change-Id: Id4ae41e4bc3fb8227367deac899878ecf9d7b98e
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/341003
Reviewed-by: Derek Sollenberger <djsollen@google.com>
Commit-Queue: Michael Ludwig <michaelludwig@google.com>
9 files changed