Allow nodes to expand until a certain condition is met.

[ghostbuster91]

Can this functionality be implemented utilising API?
To some degree, see my PR.

Is your feature request related to a problem? Please describe.
I'm always frustrated when I work with java/scala projects. In these languages directory structure should reflect the namespace hierarchy which usually results in multiple nested directories with only a single child directory.

E.g. a namespace com.example.something will have the following directory structure:

modules/src
└── main
    └── com
        └── example
            └── something
                ├── bar.txt
                └── foo.txt

Describe alternatives you've considered

I have two options if I want to explore this structure and get to the bottom of it:

1. expand nodes manually one by one until I reach the bottom
2. use expand_all function but this has following downsides:
   • when I don't know the directory structure it might result in a lot of nodes being opened unnecessarily, which I will have to close later
   • when I do know the directory structure and I know that there are some additional directories I might still use expand_all knowing that I will have to close some of them
3. use group_empty feature. I prefer to have a tree like structure. One reason for that is that it is more horizontally compact that the same structure rendered with group_empty enabled.

Describe the solution you'd like

I would like to have an option that allows me to recursively expand all directories as long as there is only one children that is also a directory. If a directory that has more children is encountered the expansion should be stopped (after expanding that directory).

This can be implemented in more generic way - expand until a certain, user provided, condition is met.