A new script, bytecode_dispatches_report.py reads the table produced
when FLAG_trace_ignition_dispatches is enabled and produces either a
report of top source-destination pairs, or a heatmap that can be
viewed interactively and saved to file.

BUG=v8:4899
LOG=N

Review URL: https://codereview.chromium.org/1869423002

Cr-Commit-Position: refs/heads/master@{#35438}