Backporting SERVER-104405 (on 8.0 & 7.0) is too complex.

Instead, for 7.0 & 8.0 (and only those versions), introduce a new CursorResponseBsonSize limit of 16MB+32KB (either in general or limited specifically to oplog cursors).

This has the advantages of being simpler and the lowest risk solution, because:

• It shouldn't break any user writes. 

• From the query side, the batch building code will stop adding new documents after we reach or exceed 16MB anyway.

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