Simplify SegmentedSwitch implementation

[sjavora]

No changes in functionality, just code simplification. No more custom builder, so there is no longer a two-view limit, but everything else should stay the same - and it seems this will work with a ForEach as well, so this is a good preparation for Tabs.

Closes #575.

[PavelHolec]

👍

[sjavora]

@PavelHolec updated everything, including the button background highlight - I just used what looked right to me, so this will probably need to be tweaked. I think we'll want to use the same thing for Tabs, so I extracted the style to a separate file.

[sjavora]

@PavelHolec please recheck - probably the whole thing. Buttons are now responsible for drawing the selected segment, so the custom style can shrink the backgournd kind of like the official component. I tried to update the fade/highlight on the unselected segments, but of course we're limited here by the fact that the buttons don't actually contain the content, but are drawn under them, so no fade of the titles and no shrinking of the titles, either.

Still, I think this is now pretty damn good, considering how much time (way more than I'd like) I spent on it. See video for what the interactions look like now.

Ideal size is also supported.

Screen.Recording.2023-05-30.at.0.20.59.mov