Improvements to component example's resizing

[juuso-vaadin]

Number of components benefit from ability to resize the rendered example area. Currently there is bit of variance across the components. It would make sense to style the split panel to be integrated part of the code example widget.

Original style

Proposed style

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[jouni]

And instead of being baked into the individual examples, this should be a feature in DSP that authors can easily toggle on when embedding an example on the page. For example:

[.example.resize-horizontal]
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