feat: add connection items without hacks

[maribethb]

Fixes #360

Implements the Connection context menu items without the hacks. Depends on RaspberryPiFoundation/blockly#8882, tests pass locally when they're linked.

Note that in core Connections don't implement the IContextMenu interface yet, so we still call the contextmenu.show method manually. Fixing that is coming soon. But this removes the hacks around including the connection in the scope and manually checking the precondition functions.