C#: Generate On{EventName} method to raise signal events

modules/mono/editor/Godot.NET.Sdk/Godot.SourceGenerators.Tests/TestData/GeneratedSources/EventSignals_ScriptSignals.generated.cs

@@ -32,6 +32,10 @@ partial class EventSignals
         add => backing_MySignal += value;
         remove => backing_MySignal -= value;
 }
+    protected void OnMySignal(string str, int num)
+    {
+        EmitSignal(SignalName.MySignal, str, num);
+    }
     /// <inheritdoc/>
     [global::System.ComponentModel.EditorBrowsable(global::System.ComponentModel.EditorBrowsableState.Never)]
     protected override void RaiseGodotClassSignalCallbacks(in godot_string_name signal, NativeVariantPtrArgs args)