Use raw MTLBuffer for texture uploads.
Use raw MTLBuffer for texture uploads.

There's a fair bit of overhead to setting up a GrMtlBuffer (adding it
to the resource cache, etc.) that isn't necessary in this case when
using a temporary buffer. Overall it gives about 10% improvement in
uploadToTexture().

Change-Id: I99449c9001098c90743cba8d614007db307156d3
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/230131
Commit-Queue: Jim Van Verth <509afb0bfbb23ecaaf1fb3323209f531b45e75a6@google.com>
Reviewed-by: Greg Daniel <39df0a804564ccb6cf75f18db79653821f37c1c5@google.com>

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