[flang][acc] Implement MappableType interfaces for fir.box and fir.array (#122495)

The newly introduced MappableType interface in `acc` dialect was
primarily intended to allow variables with non-ma

[flang][acc] Implement MappableType interfaces for fir.box and fir.array (#122495)

The newly introduced MappableType interface in `acc` dialect was
primarily intended to allow variables with non-materialized storage to
be used in acc data clauses (previously everything was required to be
`pointer-like`). One motivator for this was `fir.box` since it is
possible to be passed to functions without a wrapping `fir.ref` and also
it can be generated directly via operations like `fir.embox` - and
unlike other variable representations in FIR, the underlying storage for
it does not get materialized until LLVM codegen.

The new interface is being attached to both `fir.box` and `fir.array`.
Strictly speaking, attaching to the latter is primarily for consistency
since the MappableType interface requires implementation of utilities to
compute byte size - and it made sense that a
`fir.box<fir.array<10xi32>>` and `fir.array<10xi32>` would have a
consistently computable size. This decision may be revisited as
MappableType interface evolves.

The new interface attachments are made in a new library named
`FIROpenACCSupport`. The reason for this is to avoid circular
dependencies since the implementation of this library is reusing code
from lowering of OpenACC. More specifically, the types are defined in
`FIRDialect` and `FortranLower` depends on it. Thus we cannot attach
these interfaces in `FIRDialect`.

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