Support explicit values in flag properties, add C# flags support

- Add support for explicit values in properties using `PROPERTY_HINT_FLAGS`
that works the same way it does for enums.
- Fix enums and flags in VisualScriptEditor (it wasn't considering the
explicit value).
- Use `PROPERTY_HINT_FLAGS` for C# enums with the FlagsAttribute instead
of `PROPERTY_HINT_ENUM`.

editor/editor_properties.h

@@ -265,9 +265,9 @@ class EditorPropertyFlags : public EditorProperty {
 	GDCLASS(EditorPropertyFlags, EditorProperty);
 	VBoxContainer *vbox = nullptr;
 	Vector<CheckBox *> flags;
-	Vector<int> flag_indices;
+	Vector<uint32_t> flag_values;
 
-	void _flag_toggled();
+	void _flag_toggled(int p_index);
 
 protected:
 	virtual void _set_read_only(bool p_read_only) override;