GVST is how these probes sent data in Fenix and is now unnecessary (and doesn't send data in Fenix release) since Firefox Desktop has direct access to Glean. We therefore need to clean them up in some capacity.
Following the recommendations from the GeckoView Streaming (GVST) validation effort, this is a pure Glean api implementation of the metrics that fell under gfx and its subcategories in geckoview streaming.
Each metric retains its previous name, and gains a Glean Interface for FireFox Telemetry (GIFFT) version, such that downstream data analyses will not be impacted.
Differential Revision: https://phabricator.services.mozilla.com/D198872
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