Some recent changes to choice of translation

Since 6.7 there has been a flury of activity in how Qt choses, and helps its users chose, suitable localisation and internationalisation. That flurry seems to have settled down now, in 6.9, so it's time to give a summary of what's changed and why. The story actually starts in 6.4 with a fix for QTBUG-102796, to make the ordering of entries in uiLanguages() consistent between the system locale and those based on data from the Unicode Consortium's Common Locale Data Repository (CLDR). But first, let's get …