SkSL ByteCode: Remove specialized instructions for N up to 4

Nearly all instructions have one form, with a count byte after the
instruction. Simplifes the SkVM conversion logic, reduces code size.

Change-Id: I5ff7bb2991a09198c5c8f5bcaf2c1017c06be5d4
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/299682
Reviewed-by: Mike Klein <mtklein@google.com>
Commit-Queue: Brian Osman <brianosman@google.com>
4 files changed