Convert fir.allocmem and fir.freemem operations to calls to malloc and free, respectively

Convert fir.allocmem and fir.freemem operations to calls to malloc and free, respectively

This patch is part of the upstreaming effort from the fir-dev branch.

Address review comments
- move CHECK blocks to after the mlir code in the test file
- fix style with respect to anonymous namespaces: only include class definitions in the namespace and make functions static and outside the namespace
- fix a few nits
- remove TODO in favor of notifyMatchFailure
- removed unnecessary CHECK line from convert-to-llvm.fir
- rebase on main - add TODO back in
- get successfull test of TODO in AllocMemOp converion of derived type with LEN params
- clearer comments and reduced use of auto
- move defintion of computeDerivedTypeSize to fix build error

Co-authored-by: Eric Schweitz <eschweitz@nvidia.com>
Co-authored-by: Jean Perier <jperier@nvidia.com>
Reviewed By: awarzynski, clementval, kiranchandramohan, schweitz

Differential Revision: https://reviews.llvm.org/D114104