fix(NODE-4108): improve return type for withTransaction()

[vkarpov15]

Description

The withTransaction() function signature implies that withTransaction() returns the same value that the user-provided callback returns. But that isn't the case, it always returns something like this:

{
  ok: 1,
  '$clusterTime': {
    clusterTime: new Timestamp({ t: 1650213729, i: 1 }),
    signature: {
      hash: new Binary(Buffer.from("0000000000000000000000000000000000000000", "hex"), 0),
      keyId: 0
    }
  },
  operationTime: new Timestamp({ t: 1650213729, i: 1 })
}

Reported in Automattic/mongoose#9919

What is changing?

Function signature for withTransaction()

Is there new documentation needed for these changes?

What is the motivation for this change?

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
• New TODOs have a related JIRA ticket

[nbbeeken]

It just so happens a ticket to fix this work was next up on our scheduled queue, let me know if it would be easier for you if I took on making the changes mentioned:

[nbbeeken]

Even though the return type is meant to be an internal command result we should reflect what's actually returned here and we can fix this in the next major version. This function will return the command result if the transaction commits successfully, it will throw if it aborts and it will return undefined if it's aborted manually within the user provided function, so it's important that the result at least demonstrate that it can be truthy or not under the right circumstance.
So we should put the type in here that matches the actual result from the function, and add tests to prevent a regression.

[nbbeeken]

#3236