Fem: Add radiation heat transfer (#13466)

* FEM: Add radiation heat transfer
* FEM: Add radiation heat transfer to CalculiX writer
* FEM: Update .inp files
* Fem: Rename heat flux ui members

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Co-authored-by: FEA-eng <59876896+FEA-eng@users.noreply.github.com>

src/Mod/Fem/Gui/Command.cpp

@@ -578,6 +578,9 @@ void CmdFemConstraintHeatflux::activated(int)
     doCommand(Doc,
               "App.activeDocument().%s.FilmCoef = 10.0",
               FeatName.c_str());  // OvG: set default not equal to 0
+    doCommand(Doc,
+              "App.activeDocument().%s.Emissivity = 1.0",
+              FeatName.c_str());  // OvG: set default not equal to 0
     doCommand(Doc,
               "App.activeDocument().%s.Scale = 1",
               FeatName.c_str());  // OvG: set initial scale to 1