Support minimizing windows

[gdrbyKo1]

Hi. Thanks for the great library. I'd like to ask about a potential new feature, though. How feasible would it be to support minimizing (folding, collapsing) windows, so that once minimized, only the title bar can be seen?
Something like this:
I skimmed through the code and couldn't figure out a simple way to achieve this. There's the expand MosaicRootAction which could perhaps be used if we had a way of figuring out the required split percentage, but this sounds too much like a hack. And I can only imagine how messy it would get when handling parent element resizes.

[nomcopter]

What would it do if the windows were side by side? Agreed I don't think this is too doable with the current API. Open to requests and PRs though.

[gdrbyKo1]

It would only make sense for horizontal panes, yeah. And then another constraint could be that it shouldn't be possible to collapse all the panes in a column, because there should always be at least one element to fill the available vertical space.

[danired]

Hi!

I know this is an old issue but it would be great to have this feature 🥺