nodes: revert shader ID to string

Much easier to manage this way and fixes a compile issue on several
platforms.

app/node/generator/polygon/polygon.cpp

@@ -85,7 +85,7 @@ void PolygonGenerator::Retranslate()
   color_input_->set_name(tr("Color"));
 }
 
-ShaderCode PolygonGenerator::GetShaderCode(const QByteArray &shader_id) const
+ShaderCode PolygonGenerator::GetShaderCode(const QString &shader_id) const
 {
   Q_UNUSED(shader_id)
 

app/node/generator/polygon/polygon.h

@@ -40,7 +40,7 @@ public:
 
   virtual void Retranslate() override;
 
-  virtual ShaderCode GetShaderCode(const QByteArray& shader_id) const override;
+  virtual ShaderCode GetShaderCode(const QString& shader_id) const override;
   virtual NodeValueTable Value(NodeValueDatabase &value) const override;
 
   virtual bool HasGizmos() const override;