This moves the code that detects very low memory scenarios and grabs memory
reports from the main thread event-loop to the available memory tracker.
Besides removing the overhead of the check from the event-loop code this
increases the likeliness of the reports being gathered by sampling at a
higher frequency but only when we already detected a low-memory scenario. Last
but not least this add checks for low commit-space detection alongside low
virtual-memory detection.
Differential Revision: https://phabricator.services.mozilla.com/D3669
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extra : moz-landing-system : lando