This patch introduces a new bitcast operation for integer, float,
character, and logical.
The main rational for it is that it is currently not possible to express
such bitcast in FIR without going trough memory and there is a need to
have some bitcast support when interfacing with the memref dialect where
one cannot use fir.char<> and fir.logical and must use the underlying
storage type. Using fir.convert is not a good idea because it is a
semantic cast and it will for instance normalize integers when
converting from/to logical.
This could also be used to simplify the implementation of TRANSFER for
the cases of simple scalars of those types.
Assisted by: Claude
252eb2a743