tools/callstats-from-telemetry.sh converts multiple telemetry results
form benchmark runs into a single callstats-compatible json file.

Change-Id: I775109d4274c2cf8d87797b73695497d82d59d4a
No-Try: true
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2276043Reviewed-by: Leszek Swirski <leszeks@chromium.org>
Commit-Queue: Camillo Bruni <cbruni@chromium.org>
Cr-Commit-Position: refs/heads/master@{#68630}