Add project size-limit check on sprite-duplication

[jwzimmer-zz]

We check when the act of duplicating a costume or adding an asset from the backpack would bring the project size limit over the total size limit, but we don't check when duplicating a sprite would do so. We should add a check on sprite duplication to be consistent.

@cwillisf said:

The check that's popping up on costume duplication right now is being done at the UI level, after you pick "duplicate" but before the UI actually calls the duplication function. Sprite duplication should have a similar UI-level check but apparently doesn't...