ResourceCheck was previously using cmp.Diff on multiline goroutine stacks
The produced output was difficult to read for a number of reasons:
- the goroutines were sorted by count, and a changing count caused them to
jump around
- diffs would be in the middle of stacks
Instead, we now parse the pprof/goroutines?debug=1 format goroutines and
only diff whole stacks.
Updates #1253
Signed-off-by: Paul Scott <paul@tailscale.com>
