This enables exfiltrating Gecko scalars defined in
Gecko in products using both engine-gecko and the
Glean SDK.

Firefox Desktop policies.

It's possible that `action` parameter may be missing. This patch adds handling for that case,
and tests for the interceptor (which were missing entirely) that cover all combinations.

should be activated.

This patch does a few things:
- adds a webextension for communicating with fxa web content
- provides a backend for said webextension, which understands webchannel communication protocol
and knows how to relay messages to the account manager, and query its state
- expands account manager a bit to support the webchannel authentication protocol
- adds a (rather detailed!) AuthType parameter to AccountObserver:onAuthenticated, instead of the very vague 'newAccount' flag
Co-authored-by: Arturo Mejia <arturomejiamarmol@gmail.com>
Co-authored-by: vladikoff <vlad.filippov@gmail.com>

Preparatory work for allowing users to choose what to sync. We are about to
tie SyncConfig with FxA's "capabilities" webchannel API, which takes a set of
"engines" as strings. To simplify our integration work, this patch replaces an
untyped set of "stores" with a typed set of "engines" at the API level.

the TrackingProtectionPolicy.strict() is set.