Add additional info to BOLT graphviz CFG dumps.

Summary:
Add the following info the graphviz CFG dump:
- Edges are labeled with the jmp instruction that leads to that edge.
- Edges include the count and misprediction count.
- Nodes have (offset, BB index, BB layout index)
- Nodes optionally have tooltips which contain the code of the basic block.
  (enabled with -dot-tooltip-code)
- Added dashed edges to landing pads.

(cherry picked from FBD3646568)