move block loop into finite_volume

[oporth]

• [x] Oliver: describe here the precise steps needed for refactoring.
• [ ] Johan: will try to execute them.

[jhidding]

Reimplement finite_volume subroutine from /src/mod_finite_volume.t. The sCT parameter becomes bgT etc. This replaces the loop in mod_advance.t lines 680:705. The new function is called finite_volume_all. All w(i) references become bg%w(i) where bg%w stores data for all blocks.

!$acc loop parallel
do igrid=1,nleafstail
    call phys_to_primitive(iXI^L, ixI^L, wrpim(:,:,:,igrid), ps(igrid)%x(:,:))
end do

phys_to_primitive may need to be hardwired to hd_to_primitive_gpu from mod_hd_phys. To turn a subroutine into a device function use the !$acc routine directive.

Run agile baseline test case.