SRHD: Update cons2prim

This PR replaces the SRHD's own c2p with that of GRHD.

The following parameters are added to the SRHD section:

• id_smooth = false: If true initial data is smoothed with a Bernstein filter.
• av_regularization = "none": Controls which AV regularization is to be used.
• c2p_cold_eos_parameters = [ 100.0, 2.0 ]: Parameters of cold polytropic EoS for c2p, analogous to GRHD.
• av_drag = 0.0: AV dragging factor to control how rapid AV can change, analogous to GRHD and EulerEq.
• av_recompute_substeps = false: If true AV recomputation is triggered on every substep in the evolution.