Improve support for small/large/extra-large text sizes

[defagos]

As a user who enables larger/smaller fonts I would like the display to be tailored accordingly and the demo application to remain usable at any time.

Hints

• We should use a font modifier to size symbol-based icons in a way that scales with system text size settings.
• Some issues arise with large fonts in the Pillarbox demo, most notably with the playlist view (large button bar), with the error view (also in the playlist layout), in particular in tricky situations (e.g. playlist landscape with error).

This should be improved.

Acceptance criteria

• The demo has been updated to improve support for larger fonts.
• The smallest and extra-large setting is supported well (at least content stays with the screen bounds).

Tasks

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