[flang] Added fir.dummy_scope operation to preserve dummy arguments association. (#90642)

The new operation is just an abstract attribute that is attached to
[hl]fir.declare operations of dummy arguments of a subroutine.
Dummy arguments of the same subroutine refer to the same
fir.dummy_scope, so they can be recognized as such during FIR AliasAnalysis.
Note that the fir.dummy_scope must be specific to the runtime
instantiation of a subroutine, so any MLIR inlining/cloning should duplicate and
unique it vs using the same fir.dummy_scope for different runtime instantiations.
This is why I made it an operation rather than an attribute.
The new operation uses a write effect on DebuggingResource, same as
[hl]fir.declare, to avoid optimizing it away.