feat(NODE-3692): make change stream events typing more generic

[mrbrianevans]

Added typescript generic typing to ChangeStreamEvents

Description

What changed?
The typing for ChangeStreamEvents was not generic, and did not contain <TSchema> so it was always assumed to be of type Document. This would affect code usage like this:

interface MyDoc extends Document{
   name: string
}
const client = new MongoClient('');
const coll = client.db('test').collection<MyDoc>('test');
coll.watch().on('change', c => c.fullDocument) 
// c.fullDocument above is typed as Document, but should be MyDoc

ChangeStreamDocument already had generic types, so I just passed through <TSchema>.

I tried it out locally and the typing showed correctly in my editor.

Could someone confirm that the init and more events do indeed return the same structure as TSchema, as I do not know what these events are?

[durran]

Verified init and more events are returning the command response, which I believe can be TSchema in these cases.

[durran]

I've added type tests and opened #3034 to replace this PR.