[flang][cuda] Use fir.cuda_deallocate for automatic deallocation (#89662)

Automatic deallocation of allocatable that are cuda device variable must
use the fir.cuda_deallocate operation. This patch update the automatic
deallocation code generation to use this operation when the variable is
a cuda variable.

This patch has also the side effect to correctly call
`attachDeclarePostDeallocAction` for OpenACC declare variable on
automatic deallocation as well. Update the code in
`attachDeclarePostDeallocAction` so we do not attach on fir.result but
on the correct last op.