Everywhere: Replace Model::update() with Model::invalidate()

Most of the models were just calling did_update anyway, which is
pointless since it can be unified to the base Model class. Instead, code
calling update() will now call invalidate(), which functions identically
and is more obvious in what it does.

Additionally, a default implementation is provided, which removes the
need to add empty implementations of update() for each model subclass.

Co-Authored-By: Ali Mohammad Pur <ali.mpfard@gmail.com>

Userland/Libraries/LibGUI/JsonArrayModel.h

@@ -50,7 +50,7 @@ public:
     virtual int column_count(const ModelIndex& = ModelIndex()) const override { return m_fields.size(); }
     virtual String column_name(int column) const override { return m_fields[column].column_name; }
     virtual Variant data(const ModelIndex&, ModelRole = ModelRole::Display) const override;
-    virtual void update() override;
+    virtual void invalidate() override;
 
     const String& json_path() const { return m_json_path; }
     void set_json_path(const String& json_path);