Add trace coordinates to SkVMDebugInfo.

The SkVMDebugInfo now includes an skvm::Coord that the caller is
responsible for filling in before converting the program. If it is set,
the value indicates the device coordinates that should be traced. If it
is unset, debug traces will not be emitted at all.

Within the SkVMCodeGenerator, we now have a new traceMask() call which
combines the current execution mask with the trace mask. Tracing opcodes
now pass the result of traceMask() instead of mask(). This will limit
trace data to the selected pixel, instead of tracing the entire draw.

Bug: skia:12614
Change-Id: I1f8ce7d18a31aa60a139a4a7335c2a285d6aee60
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/472798
Commit-Queue: John Stiles <johnstiles@google.com>
Auto-Submit: John Stiles <johnstiles@google.com>
Reviewed-by: Brian Osman <brianosman@google.com>
8 files changed