Fix potential freezing browser

[AlexisCnockaert]

Due to the possible complexity of subdirectories when opening the File Browser, now it dont expand the tree when its opened.

Fixes https://github.com/pharo-project/pharo/issues/18450#issuecomment-3164391609

@ELePors is it okay for you that way ?

[Ducasse]

We could have a setting (or a configuration) to be able to have expansion on opening.

[jecisc]

Maybe we should do as in the mac Finder or the windows explorer.

We have a list of the drives but not as a tree. If you click on it, you navigate it in the right. The reason they are doing it this way might be to avoid this kind of freezes?

[Ducasse]

it would be nice to be able to decide. Because it works well on my machine. So if people have slow discs or slow network. So we could have a classVar to control the opening because opening on your folder is quite nice.

[Ducasse]

I will integrate it now and I will fix it.