Fix mismatches in CUDA execution space qualifiers between declarations and

definitions.

Add missing `KOKKOS_INLINE_FUNCTION` to the definition of:
- `FixEnforce2DKokkos::post_force_item`
- `FixNeighHistoryKokkos::zero_partner_count_item`
- `FixNeighHistoryKokkos::pre_exchange_item`

Add missing `KOKKOS_FUNCTION` to the definition of:
- `NeighborKokkosExecute::build_Item`
- `NeighborKokkosExecute::build_Item_Ghost`
- `NeighborKokkosExecute::build_ItemSize`