Eeschema: enable tunable VDC, IDC sources in sim

ADDED: Eeschema SPICE simulator now supports tuning VDC and IDC
sources.

Adds ability to interactively tune VDC and IDC sources in sim.
This allows users to quickly test bias/supply changes during
transient simulations.

eeschema/sim/sim_model_source.cpp

@@ -44,6 +44,21 @@ std::string SPICE_GENERATOR_SOURCE::ModelLine( const SPICE_ITEM& aItem ) const
     return "";
 }
 
+std::string SPICE_GENERATOR_SOURCE::TunerCommand( const SPICE_ITEM& aItem, double aValue ) const
+{
+    std::string result = "";
+
+    switch( aItem.model->GetType() )
+    {
+    case SIM_MODEL::TYPE::V: // VDC/IDC: it is clear which parameter should be used
+    case SIM_MODEL::TYPE::I:
+        result = fmt::format( "alter @{}={:g}", aItem.model->SpiceGenerator().ItemName( aItem ),
+                              aValue );
+        break;
+    default: break; // other sources: unclear which parameter the user wants
+    }
+    return result;
+}
 
 std::string SPICE_GENERATOR_SOURCE::ItemLine( const SPICE_ITEM& aItem ) const
 {
@@ -1207,3 +1222,14 @@ std::vector<std::string> SIM_MODEL_SOURCE::GetPinNames() const
     else
         return { "+", "-" };
 }
+
+const SIM_MODEL::PARAM* SIM_MODEL_SOURCE::GetTunerParam() const
+{
+    switch( GetType() )
+    {
+    case SIM_MODEL::TYPE::V: // VDC/IDC: it is clear which parameter should be used
+    case SIM_MODEL::TYPE::I: return &GetParam( 0 ); break;
+    default: break; // other sources: unclear which parameter the user wants
+    }
+    return nullptr;
+}