Minify variable names in module code.

This will rename any function parameter or local variable to single-
letter names. (The Graphite vertex code actually uses more than 52
names, so it spills over into 'aa', 'ab', 'ac', 'ad'.)

This change saves ~8.5K:

sksl_binary_size_gpu: 18335 -> 17375 bytes
sksl_binary_size_graphite: 21386 -> 13800 bytes
sksl_binary_size_compute: 245 -> 245 bytes

Bug: skia:13775
Change-Id: I3c42c090685321d5b7ff668c766351e68b79e776
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/585760
Auto-Submit: John Stiles <johnstiles@google.com>
Reviewed-by: Brian Osman <brianosman@google.com>
Commit-Queue: John Stiles <johnstiles@google.com>
16 files changed