Improve types

[Nevon]

This does two things:

Constrain the parameter types for cluster.fetchTopicOffsets

cluster.fetchTopicOffsets now has two optional parameters, fromBeginning and fromTimestamp. In reality, these are mutually exclusive. There is no case in which you would want to pass in both. Simultaneously, there is also no case in which you would not want to pass in one of them. I.e. they are mutually exclusive but required.

// Would have compiled but failed at runtime
await cluster.fetchTopicOffsets([{
  topic: 'foo',
  partitions: [{ partition: 1 }]
}])

// Would compile but behave strangely at runtime
await cluster.fetchTopicOffsets([{
  topic: 'foo',
  partitions: [{ partition: 1 }]
  fromBeginning: true,
  timestamp: 1597492814792
}])

With the updated type definition, neither of those cases are possible anymore.

Add JSDoc annotations for internal factory methods for Consumer, Producer and Admin

Some of these previously had return annotations but not all of them, and none of them had parameter annotations so everything was any, pretty much.

Unfortunately I couldn't find a way to get JSDoc to understand that params.instrumentationEmitter should be an instance of InstrumentationEventEmitter. The typedef in there didn't make any sense, so I removed that. It should just be a matter of importing the module and then just using the classname, but it doesn't seem to work in VSCode at least.

Also, there is absolutely no way to reference an enum in a @param, which I noticed when trying to type isolationLevel. Best I can do is number, which is the underlying type. You can constrain the possible values by putting literals in there (@param {(0|1|2)} isolationLevel), but that is ridiculous.