Adds new MetaMetricsController

• Moves most constants previously declared in shared/modules/metametrics to shared/constants/metametrics
• Moves all global type declarations to shared/constants/metametrics
• Changes the segmentNoop into a factory that creates a mocked module. This new mocked module should behave closer to the way that Segment's track method actually works (including queueing). This is helpful for testing purposes and means that e2e tests should timeout if we accidentally wait for events without flushImmediately set to true.
• Moves as many event/page tracking implementation details from the UI into a new MetaMetrics controller.
• Moves and migrates metaMetrics related fields from preferences controller to MetaMetrics controller.
• No longer required to have a factory for generating trackMetaMetricsEvent functions. As many details as possible are tracked in the new controller's store instead of having to be provided by the consumer of .trackEvent.
• Also adds .getNetworkIdentifier method on the network controller as it didn't' really make sense to have in the Metametrics controller.
• Adds 95%+ code coverage on the new controller, where previously the MetaMetrics implementation was untested

Rationale

As we do not have great control over performing operations before the extension UI completes exit/close events, we cannot rely on the provided segment utilities for flushing the event queue. We also have seen that even with batching disabled (setting flushAt: 1), some event loss is still occurring. By having the background process handle communication with Segment's API, we can use the batching mechanism of Segment and capture events from short-lived UI flows.