ScrollView: refactor default layout

[FrancescoCioria]

requirements

ScrollView is fluid (width/height 100%) and this brings up a problem:

• width/height 100% always refers to parent --> ScrollView doesn't take into account its children size
• max-width/height always refers to parent's width/height --> putting max-width/height on parent is useless

Take the example of Menu in PanelMenu/ContextualMenu:

• we want ScrollView to have the size of its content
• we want ScrollView to stop at some point and enable scrolling (max-width/height)

That is currently impossible.

specs

we should consider refactoring ScrollVIew to have

• width/height: auto (grow with content)

and one of these two:

• have max-width/height: 100% (don't overflow parent)
• have max-width/height: inherit (use parent's max-width/height --> throw warning if missing)

I may prefer the first one as max-width/height could always be overwritten with inline style through props (also, it's less magical)

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or simply use FlexView and require the parent to be a column FlexView!

misc

This is a breaking change --> it'll probably break some points of current layout