Backwards compat for mine.get on pre-Nitrogen minions
Backwards compat for mine.get on pre-Nitrogen minions

With this change, the master will accept `expr_form` from
its minions doing a `mine.get`, which is what minions versions
before Nitrogen would do. This solves issue #42713.

In case both `tgt_type` and `expr_form` are present, the former
gets precedence.

Performance-wise, this adds a single dict lookup for minions
running Nitrogen onwards, and two for pre-Nitrogen minions.
This is, in my opinion, acceptable.

saltstack/salt,saltstack/salt,saltstack/salt,saltstack/salt,saltstack/salt