Creates a NoNewThreadsChecker plugin that looks for the function and checks to see if it's allowed.
-Creates two allowlists - `ThreadAllows.txt` is for thread names, while `ThreadFileAllows.txt` checks for entire files where instances of `NS_NewNamedThread` should be ignored.
-If an instance of `NS_NewNamedThread` is not listed in either list, then the checker throws an error with an additional note containing a more descriptive explanation of the failure.

Differential Revision: https://phabricator.services.mozilla.com/D62635

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extra : moz-landing-system : lando