Affects Compass, VSCode, and mongosh.

1. Add a $fill aggregation stage as sugar for $setWindowFields

• $fill will support linear interpolation and carry forward for new values
• This will only support numeric and date values
• $fill will support filling by an expression
• $fill will support filling on multiple fields at once
• $fill will support partitioning

2. Write performance tests for the new aggregation stage

More details: https://docs.google.com/document/d/1VRwaXpUDTQ1OLqwBnecZPqOk7whgQE5OFsa-OhXdLFE/edit#