smarter SkColorInfo::isOpaque()
smarter SkColorInfo::isOpaque()

We already look at the alpha type.
We can look at the color type too.

This doesn't likely matter very often, as we usually have
kOpaque_SkAlphaType for opaque SkColorTypes, but might as
well toss this in there for completeness.

Change-Id: Ie164acc9294dee115d8e0637e3186a301ebe58f0
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/278479
Reviewed-by: Mike Reed <f5cabf8735907151a446812c9875d6c0c712d847@google.com>
Commit-Queue: Mike Klein <14574f09dfa9b4e14759b88c3426a495a0e627b0@google.com>

google/skia,google/skia,google/skia,aosp-mirror/platform_external_skia,aosp-mirror/platform_external_skia,google/skia,google/skia,google/skia,aosp-mirror/platform_external_skia,aosp-mirror/platform_external_skia,aosp-mirror/platform_external_skia,google/skia,google/skia,aosp-mirror/platform_external_skia,google/skia,aosp-mirror/platform_external_skia,aosp-mirror/platform_external_skia,aosp-mirror/platform_external_skia,aosp-mirror/platform_external_skia,google/skia