MOTOR-1014 Add __aenter__ and __aexit__ for AgnosticBaseCursor so that cursor can be instantiated using the context manager

[coderk17]

When I use the following code:

async with self.coll.find() as cursor:
    async for record in cursor:
        yield record

It's going to throw an AttributeError
So I added the asynchronous context manager method
so that I did not have to close the cursor when I was done with it

[ShaneHarvey]

This seems reasonable to me although I'd like to figure why it wasn't added to begin with. @coderk17 could you add some tests for find() and aggregate() to test/asyncio_tests/test_asyncio_cursor.py?

Opened MOTOR-1014 to track.

[coderk17]

Sure, the project is great and I'm using it, and I'm glad to add these unit tests. @ShaneHarvey

[coderk17]

This seems reasonable to me although I'd like to figure why it wasn't added to begin with. @coderk17 could you add some tests for find() and aggregate() to test/asyncio_tests/test_asyncio_cursor.py?

Opened MOTOR-1014 to track.

Hello, unit tests have been added and passed. @ShaneHarvey

[ShaneHarvey]

Lgtm