7.0.0-RC2: @AutoTimestamp and lastUpdated not persisting correctly with Mongo DB

[codeconsole]

Expected Behavior

@AutoTimestamp should update every save that has modified data.

Actual Behaviour

date is updated on the domain object, but not persisted to the database even when other updated properties are persisted correctly.

Steps To Reproduce

git clone --depth 1 --single-branch https://github.com/codeconsole/mongo-test && cd mongo-test && ./gradlew bootRun

Create a new User http://localhost:8080/user/create
Notate Last Updated and Modified dates.

Bug 1

Edit the user http://localhost:8080/user/edit/1 and change the name.
Notice only Last Updated is change and NOT Modified.

Bug 2

Edit the user http://localhost:8080/user/edit/1 and DO NOT change the name. Just Save
Notate Last Updated and Modified dates are BOTH modified. Neither should change because there are no updates.

The behavior with hibernate leaves both dates unchanged.
You can verify by stopping the app and checking out the h2 branch.

Example Application

https://github.com/codeconsole/mongo-test

Version

7.0.0-RC2

[codeconsole]

BUG 2, marks dirty even if it is the only property that is dirty

grails-core/grails-data-mongodb/core/src/main/groovy/org/grails/datastore/mapping/mongo/engine/codecs/PersistentEntityCodec.groovy

Lines 254 to 256 in 9434fd1

	if (entity.getPropertyByName(GormProperties.LAST_UPDATED) != null) {
	dirtyProperties.add(GormProperties.LAST_UPDATED)
	}

[codeconsole]

Strange how hasChanged() is true when $changedProperties is null. There are situations where trackChanges has yet to be called.

grails-core/grails-datastore-core/src/main/groovy/org/grails/datastore/mapping/dirty/checking/DirtyCheckable.groovy

Lines 72 to 79 in 9434fd1

	boolean hasChanged() {
	if (this instanceof EntityProxy && !((EntityProxy) this).isInitialized()) {
	return false
	}
	else {
	return $changedProperties == null || DirtyCheckingSupport.DIRTY_CLASS_MARKER.is($changedProperties) || !$changedProperties.isEmpty()
	}
	}

[codeconsole]

#15118