Code eval tool: use toast upon deletion instead of alert

[srietkerk]

Closes https://github.com/microsoft/pxt-microbit/issues/5911

I found the alert experience to be really clunky, so, as per @eanders-ms's suggestion, I've changed it so when a user deletes a criteria, they can undo it via a toast that pops up.

As part of this change, I made it so deleting a criteria just performs a soft deletion so undoing a deletion was possible.

UPDATED, latest upload target (with export working correctly): https://makecode.microbit.org/app/9b9448bb0aa4de66361394d15e8a90bb8c7b1ac5-d565522e6f--eval