Use bilinear mapper for states?

From a conversation earlier with @mvertens , it seemed like CMEPS is currently using area conservative mapping for states as well as fluxes, at least for some components (e.g., lnd -> atm). This differs from the CESM behavior with CPL7, which used bilinear mapping for states. It seems like this should either be changed to match the CESM behavior with CPL7 or be presented for broader scientific review and approval.

@mvertens I am not trying to suggest any particular urgency by opening this issue, but I thought it would be helpful to have issues to track outstanding discrepancies between CMEPS and CPL7.