Add a simpleperf to Gecko profile format converter

Gecko Profile Format can be used in https://profiler.firefox.com/, which
is a very powerful multi-thread profiler UI.

The format is documented here:
https://github.com/firefox-devtools/profiler/blob/main/docs-developer/gecko-profile-format.md

I have commandeered some metadata fields to show Android-specific data
in the Firefox Profiler UI:

- Timestamp
- Build ID
- Simpleperf command line

The golden test data was generated with pretty-printing with `jq`:

$ ./gecko_profile_generator.py
test/testdata/perf_with_interpreter_frames.data | jq >
test/testdata/perf_with_interpreter_frames.firefox.json

BUG=200472654
Test: Ran test/test.py -p TestGeckoProfileGenerator.\* and opened in
Firefox Profiler.

Change-Id: I53c5dd5415a0d34dbbdd45fa3031d5b66edc072d
5 files changed