[LFRic] Signify when kernel fields require up-to-date halos.

[mo-joshuacolclough]

For the adjoint of stencil operations we have decided on a lookup table approach as a first step. This produces integer fields which are passed into the adjoint kernels, and used to apply the adjoint order of operations.

The lookup table acts as a stencil operation, so it expects that the fields being used in calculations have up-to-date halo information. It is my understanding that there is no way to signify this to PSyclone apart from through using a stencil, which isn't needed in this case. Currently these lookup table kernels are written as PSy-KAl lite code, with halo exchanges added where needed.

Linked LFRic-apps ticket

• LFRic-apps ticket #597