Constructor tactics backtracking is done using [Tacticals.New] rather than [Proofview].

The primitives in [Tacticals] respect Ltac's error level, whereas the one in [Proofview] do not necessarily. In that case the error caught was ignored causing arbitrary error level after [constructor] to be canceled.

Needed the addition of an [ORD] variant to [OR] in [Tacticals.New] to avoid unnecessary precomputation (the 'D' stands for 'delay').

Fixes #3838.