oops: assignCursorPrefix does not strip the suffix

That caused exprs to assign anything starting with their prefix to the prefix
Sugar: Propagate user-given annotations from original expr into Sugar.Expression
GUI is hard-coded to use ExpressionN with ()
Sugar.MStorePoint
Sugar.Definition[U/N] are parameterized on ()
Sugar.makeTypeInfo: Can do annotations
GUI uses ExprGuiM.Payload and SugarExpr
Use SugarExpr/ExprGuiM.Payload instead of rHiddenGuids
Collapsed expressions steal the payloads of the expanded terms.

The collapsed expression will get marked.