Add support for insertion markers wrapping blocks mid stack

[BeksOmega]

Check for duplicates

• I have searched for similar issues before opening a new one.

Problem

Scratch's insertion markers will wrap blocks mid stack:

However this is not supported in core blockly:

Because it requires monkey patching the connection: connect and doDragChecks which now lives in the connection checker. It also requires patching the insertion marker manager. See this discussion for more info: #6876 (comment)

Request

Add support for insertion markers wrapping blocks mid stack.

No clue what APIs we would need to actually implement this though. I think the first patch is especially complicated, because it lives in the connection code and is incompatible with the current behavior.

Alternatives considered

N/A

Additional context

Linking the original discussion that surfaced this issue again: #6876 (comment)