[flang] Fix INQUIRE of access and formatting possibilities

Don't give false positives from INQUIRE about possible
access mode changes on connected units.  DIRECT and SEQUENTIAL
cannot be intermixed, apart from allowing DIRECT on a SEQUENTIAL
file with fixed-size records and positioning.  Nor can
FORMATTED and UNFORMATTED be interchanged.  On unconnected
files, the best that we can do is "UNKNOWN".

Differential revision: https://reviews.llvm.org/D88673