Translations: Improve interoperability with *.qm/*.ts files

Although Qt DS can export *.json translation files to traditional *.ts files (https://doc.qt.io/qtdesignstudio/studio-translations.html#generating-qt-translation-source-files ), the *.json files have much narrower scope than *.ts.

For now, I have linked other tickets required to bring the Qt Design Studio Multi-lang DB up to feature parity with Qt Linguist files.

However, maybe the better route is to make use of the existing *.ts format rather than trying to implement a new format from scratch? QDS-1520 was closed as "out-of-scope", but won't that route take less effort than getting the *.json format up to feature parity? Note also that the CMake translation API (https://doc.qt.io/qt-6/qtlinguist-cmake-qt-add-translations.html ) means that developers no longer need to run lrelease, so we only really need lupdate (or a Qt-DS compatible alternative) to work.