fix(NODE-3515): do proper opTime merging in bulk results

[durran]

Description

This is a forward port to 4.1 branch for NODE-3515.

Fixes the merging of results in a bulk write inside a transaction to properly compare and set the opTime value in the result.

What is changing?

Per various specifications, lastOp and opTime are optional fields in results that can be either a Timestamp, or an object with a ts and t property of Timestamp and Long respectively. In some cases they are both Longs. Our comparison logic on these values could get into a hot mess when trying to compare values of different types. This changes the opTime value in the bulk write result to always be an object with the ts and t fields and never sets it as a Timestamp value anymore.

Is there new documentation needed for these changes?

No

What is the motivation for this change?

This was reported as a bug in HELP-28460 and related to NODE-3515, although the user provided patch did not solve all potential cases.

Double check the following

• Ran npm run check:lint script
• Self-review completed using the steps outlined here
• PR title follows the correct format: <type>(NODE-xxxx)<!>: <description>
• Changes are covered by tests

[nbbeeken]

Pending assertions from the 3.x branch

[dariakp]

Just need to update the test case names to match the assertions