Add variable slot information to SkVMDebugInfo.

This assigns a human-readable name to a debug slot. The slot map is
emitted into skslc output files, and will be used in the future to
display human-readable names in the debugger.

Change-Id: I288358de305239005faa5814bd1d77a38b5e05b0
Bug: skia:12614
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/470400
Commit-Queue: John Stiles <johnstiles@google.com>
Commit-Queue: Brian Osman <brianosman@google.com>
Auto-Submit: John Stiles <johnstiles@google.com>
Reviewed-by: Brian Osman <brianosman@google.com>
11 files changed