test(NODE-5327): fix handling of embedded nulls in spec runner matcher

[durran]

Description

Updates the spec test runner matcher to handle null or root fields and embedded fields differently.

What is changing?

• Allows for a root field in a matcher defined in the spec assertion as null to match on both null or undefined.
• Changes embedded field assertions to test for exact matches.

With this change, here is a patch showing the expected ecc collection assertions would have failed before they were removed: https://spruce.mongodb.com/task/mongo_node_driver_next_rhel80_large_Node20_test_7.0_sharded_cluster_patch_dc068ac1f6e91794836e103f8a06c2580405ad76_648c8bd132f4173ed7500378_23_06_16_16_20_34/tests?execution=0&sortBy=STATUS&sortDir=ASC

Is there new documentation needed for these changes?

None

What is the motivation for this change?

NODE-5327

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