use rect-memset in legacy rect blit
use rect-memset in legacy rect blit

Timing filteredrect_nofilter bench

before:
  13/13  MB	38	6.59µs	6.6µs	6.73µs	7.02µs	3%	▆▆▆█▁▁▁▁▁▁	8888

after:
  13/13  MB	49	4.96µs	4.97µs	5.08µs	5.34µs	3%	▆▆▆█▁▁▁▁▁▁	8888

Change-Id: I1bc5a9add7918c91b79ad42ef792f27a5e133cbd
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/214866
Reviewed-by: Mike Klein <14574f09dfa9b4e14759b88c3426a495a0e627b0@google.com>
Commit-Queue: Mike Reed <f5cabf8735907151a446812c9875d6c0c712d847@google.com>

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