Handle underscores in use counter method names

[BenWu]

This is failing with

Traceback (most recent call last):   File "<frozen runpy>", line 198, in _run_module_as_main   File "<frozen runpy>", line 88, in _run_code   File "/app/probe_scraper/runner.py", line 906, in <module>     main(   File "/app/probe_scraper/runner.py", line 707, in main     upload_paths += load_moz_central_probes(
                    ^^^^^^^^^^^^^^^^^^^^^^^^
  File "/app/probe_scraper/runner.py", line 319, in load_moz_central_probes
    revision_probes = parse_moz_central_probes(revision_data)
                      ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/app/probe_scraper/runner.py", line 218, in parse_moz_central_probes
    results = PARSERS[probe_type].parse(paths, details["version"], channel)
              ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/app/probe_scraper/parsers/histograms.py", line 88, in parse
    parsed_probes = list(histogram_tools.from_files(filenames))
                    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/app/probe_scraper/parsers/third_party/histogram_tools.py", line 666, in from_files
    histograms = parser(filename)
                 ^^^^^^^^^^^^^^^^
  File "/app/probe_scraper/parsers/third_party/histogram_tools.py", line 551, in from_UseCounters_conf
    return usecounters.generate_histograms(filename)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/app/probe_scraper/parsers/third_party/usecounters.py", line 57, in generate_histograms
    for counter in read_conf(filename):
  File "/app/probe_scraper/parsers/third_party/usecounters.py", line 48, in parse_counters
    raise ValueError("error parsing %s at line %d" % (conf_filename, line_num))
ValueError: error parsing /app/probe_cache/hg/1e704c6738f494b411bce8840fcabc790f704e8b/dom/base/UseCounters.conf at line 543

mozilla-firefox/firefox@546b6eb added methods with underscores and changed the function to allow underscores. The parse_counters function here is being updated to match the one in firefox