OperationContext defines two fields which track the operation's maximum allowable latency: _deadline and _maxTime. Their documentation suggests (roughly) that _deadline is the source of truth for latency enforcement and that _maxTime contains the user-supplied value which informs the choice of deadline. However, there are cases where calling code tries to influence _maxTime in order to affect operation latency, which results in unexpectedly long operation before timeout (e.g. SERVER-108581).

Clarify what roles these fields play in documentation and in the API OperationContext exports. Ideally, collapse these (and potentially other) fields into a single concept of maximum operation latency to prevent future confusion.