rename the VM blitter to SkVMBlitter

Change-Id: I71ae924d32dc2268cc4a3db1920c08287533f9ae
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/430697
Reviewed-by: Brian Osman <brianosman@google.com>
Commit-Queue: Herb Derby <herb@google.com>
7 files changed