Add SkCapabilities object

This describes the capabilities of a particular Skia rendering context
(GPU context, or the CPU backend). At the moment, it only contains the
supported SkSL version (with a new enum added to specify the current
value as "100" and a new ES3 value as "300".

SkCapabilities can not be retrieved from an SkCanvas - the client must
have a concrete way of knowing what their destination device that will
do the actual rendering is (GrCaps or SkSurface).

This CL doesn't make use of the SkCapabilities yet, that's coming in
follow-up CLs that alter the SkSL compiler and SkRuntimeEffect API.

Bug: skia:11209
Change-Id: I4e9fd21ff7ffd79f1926c5c2eb34e10b3af4bc9b
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/537876
Reviewed-by: Michael Ludwig <michaelludwig@google.com>
Reviewed-by: Brian Salomon <bsalomon@google.com>
Commit-Queue: Brian Osman <brianosman@google.com>
Reviewed-by: John Stiles <johnstiles@google.com>
31 files changed