mesh: add const-ness to FaceInfo funcs
mesh: add const-ness to FaceInfo funcs

bwspenc/moose,milljm/moose,bwspenc/moose,idaholab/moose,bwspenc/moose,lindsayad/moose,laagesen/moose,SudiptaBiswas/moose,milljm/moose,bwspenc/moose,dschwen/moose,SudiptaBiswas/moose,andrsd/moose,idaholab/moose,dschwen/moose,laagesen/moose,milljm/moose,idaholab/moose,harterj/moose,sapitts/moose,jessecarterMOOSE/moose,milljm/moose,harterj/moose,dschwen/moose,andrsd/moose,idaholab/moose,nuclear-wizard/moose,bwspenc/moose,jessecarterMOOSE/moose,jessecarterMOOSE/moose,harterj/moose,sapitts/moose,sapitts/moose,SudiptaBiswas/moose,lindsayad/moose,dschwen/moose,andrsd/moose,SudiptaBiswas/moose,sapitts/moose,harterj/moose,jessecarterMOOSE/moose,andrsd/moose,SudiptaBiswas/moose,andrsd/moose,laagesen/moose,nuclear-wizard/moose,idaholab/moose,lindsayad/moose,lindsayad/moose,harterj/moose,laagesen/moose,nuclear-wizard/moose,jessecarterMOOSE/moose,laagesen/moose,lindsayad/moose,sapitts/moose,milljm/moose,dschwen/moose,nuclear-wizard/moose