added byte type support to SkSLC MSL generator
added byte type support to SkSLC MSL generator

Also cleaned up converting half to float

Bug: skia:
Change-Id: I4fbb01b887b40f9e6b8cf5cdd7e03e056b29db07
Reviewed-on: https://skia-review.googlesource.com/142582
Reviewed-by: Ethan Nicholas <d2cfb8c2f603266f4dc3a6f09acbcc0089603b37@google.com>
Commit-Queue: Timothy Liang <ee877cb86459160b3b88048df2ae3e60e3616bf5@google.com>

HalCanary/skia-hc,rubenvb/skia,rubenvb/skia,google/skia,HalCanary/skia-hc,google/skia,aosp-mirror/platform_external_skia,aosp-mirror/platform_external_skia,HalCanary/skia-hc,aosp-mirror/platform_external_skia,HalCanary/skia-hc,rubenvb/skia,google/skia,Hikari-no-Tenshi/android_external_skia,Hikari-no-Tenshi/android_external_skia,HalCanary/skia-hc,google/skia,google/skia,aosp-mirror/platform_external_skia,google/skia,google/skia,rubenvb/skia,aosp-mirror/platform_external_skia,Hikari-no-Tenshi/android_external_skia,Hikari-no-Tenshi/android_external_skia,HalCanary/skia-hc,rubenvb/skia,aosp-mirror/platform_external_skia,HalCanary/skia-hc,HalCanary/skia-hc,HalCanary/skia-hc,rubenvb/skia,Hikari-no-Tenshi/android_external_skia,rubenvb/skia,Hikari-no-Tenshi/android_external_skia,HalCanary/skia-hc,rubenvb/skia,rubenvb/skia,rubenvb/skia,aosp-mirror/platform_external_skia,google/skia,aosp-mirror/platform_external_skia,Hikari-no-Tenshi/android_external_skia,google/skia,aosp-mirror/platform_external_skia,aosp-mirror/platform_external_skia,google/skia,Hikari-no-Tenshi/android_external_skia