Cut 4.20.0 and write what the store says about it

[andiwand]

The changelog heading closes so the release run can find the section, and the release notes are written in all fifteen locales.

What 4.20.0 is

Everything since 4.19.1: the rebuilt editing UI, a pdf's markup tools, one-tap cell editing, and core 7.1.0 through 7.2.1 under all of it.

The store copy

scripts/store-copy.py v4.20.0 wrote it - the English from the changelog section, then one translation per locale. Play takes 500 characters and refuses the release over it; the longest here is German at 478, the English 351.

You can now edit PowerPoint files, spreadsheet cells and plain text, with undo and redo. The page stays where it was.

Highlighting is free, in documents and in PDFs. Hold an editing button to see the colours it uses.

Marking text in a PDF no longer hides it, and a mark covers the whole passage.

A wide PDF page zooms out until it fits the screen.

scripts/store-listing.py --version v4.20.0 passes: all 15 locales present.

Merging this is what lets release.yml be dispatched with version: v4.20.0.