[Request] Add Tabs (in unity GUILayout.Toolbar)

[Dragon-0609]

Let's say, I have a script that has lots of serialized fields. I want to organize them. They're split to parts (in vertical order), but with tabs, they might be organized much better.

In the example below, there're 2 tabs. First is Default for fields that weren't specified. Another is Conifg. In config I keep a lot of things like speed, duration, delay and etc, that is specified just once.