feat: have the gesture use a dragger for blocks

[BeksOmega]

The basics

• I validated my changes

The details

Resolves

Work on #7844

Proposed Changes

Upgrades the gesture class to use a IDragger for dragging blocks instead of using a IBlockDragger. This conforms to our new design for handling dragging.

Test Coverage

Manually tested with all of the previous PRs, and everything seems to wire together correctly! Once this is in I can hammer it more.

Documentation

N/A

Additional Information

As I write the other IDraggables I'll migrate the gesture to pass those to the dragger instead of using special draggers. (i.e. the workspaceDragger and bubbleDragger)

[rachel-fenichel]

I'm probably missing context, but: why does this function continue to exist but always return an empty list? Will you re-implement it later?

[BeksOmega]

Mmm I left this like this because I wasn't quite sure what to do with it, since the draggable doesn't have APIs for getting insertion markers, cuz that's super specific to blocks. But I think I can reimplements this by just walking the workspace and checking for any blocks that are flagged as insertion markers. I'll check where this is getting called from and whether that's going to be a performance killer or not.

[BeksOmega]

So it turns out that getInsertionMarkers is only called from workspace.render, so I just moved the relevant logic into there. Performance impact shouldn't be an issue, because we don't actually call that method. And if people are calling it and run into problems, I can give them more performant ways of triggering rerenders.