[flang][codegen] Add a conversion for `!fir.coordinate_of` - part 1

This patch extends the `FIRToLLVMLowering` pass in Flang by adding a
hook to transform `!fir.coordinate_of` into a sequence of LLVM MLIR
instructions.

The following cases are currently supported:
  1.  the input object is a `!fir.complex` (wrapped in e.g. `!fir.ref` or
      `!fir.box`)
  2.  the input object is wrapped in a `!fir.box` (including e.g.
      `!fir.array`).
Note that `!fir.complex` inside a `!fir.box` falls under case 1. above
(i.e. it's a special case regardless of the wrapping type).

This is part of the upstreaming effort from the `!fir-dev` branch in [1].

Differential Revision: https://reviews.llvm.org/D114159



Co-authored-by: Jean Perier <jperier@nvidia.com>
Co-authored-by: Eric Schweitz <eschweitz@nvidia.com>
Co-authored-by: V Donaldson <vdonaldson@nvidia.com>