Node's change stream tryNext helper doesn't process change stream events (by calling the _processChange) helper, so the resume token for the change stream is not updated when a change is returned to the user.  This has been the behavior since tryNext was implemented (https://github.com/mongodb/node-mongodb-native/commit/634ae4f93013c824bc153f132f0dd6c9bd2cc127).  

This can cause a number of issues

• change streams aren't resumed properly if users are relying on `tryNext` in a loop
• change streams can produce duplicate change events

I believe this wasn't caught with existing tests for a few reasons:

• our change stream test coverage isn't exhaustive (there is no test for resumability that checks for duplicate resume events).
• our unified tests only test the `next` helper
• most importantly, the resumability tests only test resuming on a single change event after initializing the change stream.  this is important because the `aggregate` call always sets the postBatchResumeToken if present, so a change stream that errors on the first change and resumes will resume properly and receive no duplicate events.

Use Case

As a... user of the tryNext api
I want... resume tokens to be updated correctly on change events
So that... I can resume the change stream from the correct point in time

User Experience

• See NODE-7042

Dependencies

• N/A

Risks/Unknowns

• N/A

Acceptance Criteria

Implementation Requirements

• make change stream's tryNext update the resume token while processing changes

Testing Requirements

• Integration test to ensure that tryNext updates the resume token

Documentation Requirements

• Update docs to update unreliability callout for tryNext, noting that it's only present up to version 6.19.0 (double check against fix version)

Follow Up Requirements

• N/A