feat(NODE-5243): add change stream split event

[durran]

Description

Adds support for change stream split events.

What is changing?

• Adds the new ChangeStreamSplitEvent type.
• Adds the splitEvent to the change stream common document type.
• Add the new prose test to test the event splitting. (see https://github.com/mongodb/specifications/tree/master/source/change-streams/tests#prose-tests #19)

Is there new documentation needed for these changes?

None

What is the motivation for this change?

NODE-5243

Release Highlight

Support for change stream split events

When change stream documents exceed the max BSON size limit of 16MB, they can be split into multiple fragments in order to not error when sending events over the wire. In order to enable this functionality, the collection must be created with changeStreamPreAndPostImages enabled and the change stream itself must include an $changeStreamSplitLargeEvent aggregation stage. This feature requires a minimum server version of 7.0.0.

Example:

await db.createCollection('test', { changeStreamPreAndPostImages: { enabled: true }});
const collection = db.collection('test');
const changeStream = collection.watch([{ $changeStreamSplitLargeEvent: {} ], {
  fullDocumentBeforeChange: 'required'
});

for await (const change of changeStream) {
  console.log(change.splitEvent); // If changes over 16MB: { fragment: n, of: n }
}

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
  • Example: feat(NODE-1234)!: rewriting everything in coffeescript
• Changes are covered by tests
• New TODOs have a related JIRA ticket

[baileympearson]

minor comment, LGTM

[baileympearson]

can we move the close logic here into the afterEach hook?

[durran]

Done