Bug 1705720 - Ensure the dispatcher is always available

[Dexterp37]

This guarantees the dispatcher is always available even before the Glean initialization. We need this because our APIs can be used before initialization, to perform fast recording of metrics.

[brizental]

Would you mind also adding a simple test to ensure this behaviour?

[brizental]

Why does this need to be null? Can't we initialize the dispatcher on the Context's constructor?

[Dexterp37]

This needs to be null because we can't really tear down the whole Context when we reset Glean, because we need to retain the storage. So we do a "soft reset" by nulling out the dispatcher in testReset

[brizental]

nit: I would prefer private _dispatcher?: Dispatcher;, but no strong requirement for this change.

[Dexterp37]

That makes it undefined though,

[brizental]

Yes, but this a very philosophical thing (null vs undefined) and makes no real difference here. Feel free to ignore the request ;)

[Dexterp37]

Would you mind also adding a simple test to ensure this behaviour?

Now that we're properly resetting, all the tests fail without the fix (instantiating the dispatcher if not available). Any test I might add would basically be the same, but let me see what I can pull off