Fix#6754 incorrect date truncation logic in JavaScript transform truncDate

[leehaut]

Fix #6754 -- JavaScript transform plugin truncDate functionality changed and does not match documentation

This PR fixes an issue in the truncDate implementation used by the JavaScript transform.
The previous implementation only reset the specific time field for the requested truncation

[mattcasters]

Can you confirm that we now implemented the other options, truncation levels, correctly and that previous functionality still works as is? It would be amazing if we had an extra integration test to show this.

[leehaut]

Can you confirm that we now implemented the other options, truncation levels, correctly and that previous functionality still works as is? It would be amazing if we had an extra integration test to show this.

I verified this through the ScriptValuesAddedFunctionsTest unit test. I will add an integration test for this

[leehaut]

Add integration test for 0066-script-javascript-truncDate.

[mattcasters]

Thanks @leehaut, great work!