Accept @[], ~[], &[] as synonyms for []/@, []/~, []/& #2747
Description
This is part of Issue #2653.
The postfix slash vector notation is awful. We are going to start accepting prefix notation as a special case notation for evecs as a transitional step (in effect, treating [] in certain contexts as a "dynamically sized type"; this analogy will become more true as we remove old uses of []). Syntax for fixed length vector types is still up in the air.