[flang] Modify right modes for READ/WRITE vs OPEN

When a mode flag is modified (e.g., BLANK='ZERO') in an I/O data transfer
statement, ensure that the right set of mode flags is modified.
There's one set of mode flags that are captured by an OPEN
statement and maintained in the connection, and another that
is maintained in an I/O statement state record for local mutability.
Some I/O API routines were unconditionally modifying the persistent
set of flags.

Differential Revision: https://reviews.llvm.org/D118835