Docs examples 14/14: Rework progress and utility examples

Part 14 of 14, the last MR in the stack that splits up the approved draft !6295 (closed) into reviewable pieces. The content is exactly what was reviewed there; I've only sliced it.

Related to #3575.

Pages: progress bar, spinner, infinite scroll, and the five utility pages (truncate, truncate text, sprintf, intersperse, friendly wrap). Realistic content, contextual placement, and unique example titles.

Once this merges, the combined stack reproduces the full diff of the draft MR exactly.