Mjolnir imports private Synapse function synapse.util.glob_to_regex, which has moved as of (unreleased) v1.50.0rc1

[reivilibre]

Describe the bug
Mjolnir imports synapse.util.glob_to_regex which has moved in Synapse v1.50.0rc1 (matrix-org/synapse#11687) to matrix-common (https://github.com/matrix-org/matrix-python-common/).

To Reproduce
Steps to reproduce the behavior:

1. Install v1.50.0rc1 (not yet released) or current Synapse develop branch with Mjolnir
2. Start Synapse
3. Synapse does not start; logs below generated

Additional context

  File "/usr/local/lib/python3.7/runpy.py", line 193, in _run_module_as_main
    "__main__", mod_spec)
  File "/usr/local/lib/python3.7/runpy.py", line 85, in _run_code
    exec(code, run_globals)
  File "/home/synapse/src/synapse/app/generic_worker.py", line 514, in <module>
    main()
  File "/home/synapse/src/synapse/app/generic_worker.py", line 510, in main
    start(sys.argv[1:])
  File "/home/synapse/src/synapse/app/generic_worker.py", line 424, in start
    config = HomeServerConfig.load_config("Synapse worker", config_options)
  File "/home/synapse/src/synapse/config/_base.py", line 461, in load_config
    obj, _ = cls.load_config_with_parser(config_parser, argv)
  File "/home/synapse/src/synapse/config/_base.py", line 533, in load_config_with_parser
    config_dict, config_dir_path=config_dir_path, data_dir_path=data_dir_path
  File "/home/synapse/src/synapse/config/_base.py", line 725, in parse_config_dict
    data_dir_path=data_dir_path,
  File "/home/synapse/src/synapse/config/_base.py", line 347, in invoke_all
    res[config_class.section] = getattr(config, func_name)(*args, **kwargs)
  File "/home/synapse/src/synapse/config/spam_checker.py", line 52, in read_config
    self.spam_checkers.append(load_module(spam_checker, config_path))
  File "/home/synapse/src/synapse/util/module_loader.py", line 49, in load_module
    module = importlib.import_module(module_name)
  File "/home/synapse/env-py37/lib/python3.7/importlib/__init__.py", line 127, in import_module
    return _bootstrap._gcd_import(name[level:], package, level)
  File "<frozen importlib._bootstrap>", line 1006, in _gcd_import
  File "<frozen importlib._bootstrap>", line 983, in _find_and_load
  File "<frozen importlib._bootstrap>", line 967, in _find_and_load_unlocked
  File "<frozen importlib._bootstrap>", line 677, in _load_unlocked
  File "<frozen importlib._bootstrap_external>", line 728, in exec_module
  File "<frozen importlib._bootstrap>", line 219, in _call_with_frames_removed
  File "/home/synapse/env-py37/lib/python3.7/site-packages/mjolnir/__init__.py", line 1, in <module>
    from .antispam import AntiSpam
  File "/home/synapse/env-py37/lib/python3.7/site-packages/mjolnir/antispam.py", line 17, in <module>
    from .list_rule import ALL_RULE_TYPES, RECOMMENDATION_BAN
  File "/home/synapse/env-py37/lib/python3.7/site-packages/mjolnir/list_rule.py", line 16, in <module>
    from synapse.util import glob_to_regex
ImportError: cannot import name 'glob_to_regex' from 'synapse.util' (/home/synapse/src/synapse/util/__init__.py)