[tools] Further improve grokdump

- Add long command names for better first-time experience
- Try to auto-detect the context object on the stack
- Mark free space object ranges
- Add print/p command to evaluate arbitrary python code
- Address expressions can now be arbitrary Python expression with auto
  register substition
- New dso command finds possible HeapObjects on the stack/memory
- New dsa command prints PushStackTraceAndDie message and values

Change-Id: I0f178077f0ccef887aa3fdd2d2d2d732925948ea
NOTRY=true

Change-Id: I0f178077f0ccef887aa3fdd2d2d2d732925948ea
Reviewed-on: https://chromium-review.googlesource.com/468866
Commit-Queue: Camillo Bruni <cbruni@chromium.org>
Reviewed-by: Jakob Kummerow <jkummerow@chromium.org>
Cr-Commit-Position: refs/heads/master@{#44430}