fix: reset initial connections before storing new ones

[mikeharv]

The basics

• I validated my changes

The details

Resolves

Fixes:

1. With two connected blocks on the workspace, move one to a different connection and commit the move.
2. Start moving the same block again, but hit escape before committing.

block_svg.ts:313 Uncaught HierarchyRequestError: Failed to execute 'appendChild' on 'Node': The new child element contains the parent.
    at BlockSvg.setParent (block_svg.ts:313:44)

Proposed Changes

This change guarantees that we clear any stored initial connections before storing new ones.

Reason for Changes

The workspace could become completely unresponsive if a revert fails. In this case, after storing an initial child connection, the block was moved to a parent connection on the same block. When the next move occurs, the initial child connection was not cleared, resulting in two conflicting initial connections. Revert would then try to "re-connect" the blocks in two conflicting ways.

Test Coverage

Thanks to @maribethb for writing a new test that ensures we don't throw when a block move is reverted after storing both a child and parent connection for two different moves.

Additional Information

Alternative to #9980

It still seems like there is some cleanup that is missing (that endDrag does but revertDrag doesn't, but this can wait for now.