fix: drag & drop issues

[matthewlipski]

This PR fixes 3 additional issues with drag & drop that we didn't previously catch:

1. When using the multi-column extension, it's possible to drag a block and drop it next to itself. BlockNote will attempt to create 2 columns containing the same block, but will throw an error it tries to remove the same block twice. This edge case has been fixed and now, nothing happens.
2. It's possible that a dragged block is dropped in an element that is not a valid drop target. In this case, only a dragend event fires, and not a drop. Since we only clear view.dragging on drop events, BlockNote will throw an error the next time the user attempts to drag a block, as it will think that a block is already being dragged. Therefore, this has been fixed by making view.dragging get cleared on dragend events instead.
3. When pasting content from the clipboard (via paste or drop events), the UniqueID plugin sets transformPasted = true. This signals that any pasted blocks should have their IDs reset & re-generated. After the IDs are reset, transformPasted is reset back to false. However, transformPasted doesn't get called at all when external content, such as files, is pasted. This means that if external content is pasted, it remains true for any subsequent drop events, causing errors as the dragged block has no ID. This has been changed so that transformPasted is always set to true or false before the subsequent paste or drop.

Closes #1444
Closes #1451
Closes #1382

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[YousefED]

great fix that actually gets rid of the hacky settimeout!