MRF: compressible energy eqn

Cross-ref: EP#2410

The work done by the MRF was not taken into account in compressible energy eqns. This has been added as:

if (MRF.active())
{
    EEqn += fvc::div(MRF.phi(), p);
}

This requires users to specify an addition divScheme

div(phiMRF,p) Gauss ...

Note: added as an if-block instead of inline in the EEqn so as not to require the additional scheme entry for non-MRF cases.

The effect can be seen in the total temperature prediction below for a compressor case

The left image shows v2312 (and earlier) behaviour, and the right shows the new behaviour, where the work done increases the temperature (as it should).