[flang] Inline scalar-to-scalar TRANSFER for same-size trivial types (#191589)
Inline the TRANSFER intrinsic for scalar-to-scalar cases where the
result is a trivial type (integer, real, etc.) and source and result
have the same storage size. Instead of calling _FortranATransfer, the
lowering now emits a fir.convert on the source address followed by a
fir.load, effectively performing a reinterpret cast.