Add SkVMDebugTracePlayer::getCurrentLineInStackFrame.

While working on the debugger, I realized that we had no interface for
getting the current line of any stack frame other than the currently-
executing frame. This can be useful for letting users explore the call
chain on the stack.

(While I was here, I also renamed `tidy` to `tidyState` in order to
match the Typescript implementation.)

Change-Id: Ife8c30d81adc17389a109698e3fba7f93e523e9e
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/496886
Auto-Submit: John Stiles <johnstiles@google.com>
Reviewed-by: Brian Osman <brianosman@google.com>
Commit-Queue: John Stiles <johnstiles@google.com>
3 files changed