Initial checkin of SkSL lexical analyzer generator (not actually in use yet).

Bug: skia:
Change-Id: I283feb9ac1cef134588204107ea019ce657e37b3
Reviewed-on: https://skia-review.googlesource.com/42084
Commit-Queue: Ethan Nicholas <ethannicholas@google.com>
Reviewed-by: Brian Salomon <bsalomon@google.com>
14 files changed