add HasValueTypeConstraint check

Author: hi-xiaoxin

src/SourceGeneration.Reflection.SourceGenerator/Models/SourceTypeParameterInfo.cs

@@ -5,6 +5,7 @@ internal class SourceTypeParameterInfo
     public string Name;
 
     public bool HasUnmanagedTypeConstraint;
+    public bool HasValueTypeConstraint;
 
     public bool HasTypeParameterInConstraintTypes;
     public string[] ConstraintTypes;