Modernize QQmlApplicationEngine's automatic translation feature

According to https://doc.qt.io/qt-6/qqmlapplicationengine.html#details,

• QQmlApplicationEngine automatically loads translation files from an i18n directory adjacent to the main QML file and the translation files must have "qml_" prefix e.g. qml_ja_JP.qm
• Translations are reloaded when the QJSEngine::uiLanguage / Qt.uiLanguage property is changed.

Example

project(QmlTranslationStudy VERSION 0.1 LANGUAGES CXX)
find_package(Qt6 6.7 REQUIRED COMPONENTS Quick LinguistTools)

qt_standard_project_setup(
    I18N_TRANSLATED_LANGUAGES de
    REQUIRES 6.7
)
qt_add_executable(appQmlTranslationStudy
    main.cpp
)
qt_add_qml_module(appQmlTranslationStudy
    URI MyApp
    VERSION 1.0
    QML_FILES
        Main.qml
)
qt_add_translations(appQmlTranslationStudy)

Problem
The current rules in QQmlApplicationEngine do not align with the default structure produced by our current CMake API. The attached example would produce the following:

• :/qt/qml/MyApp/Main.qml
• :/i18n/QmlTranslationStudy_de.qm
• :/i18n/QmlTranslationStudy_en.qm

i.e. There is no "i18n directory adjacent to the main QML file", and the *.qm files don't start with "qml_".

Suggestions

• Update the rules to look in ":/i18n" by default for *.qm files
• Auto-search for *.qm files that are named after the current project? (although I'm not sure how the CMake project name could be passed to the engine at runtime)
• Add CMake API to specifically add translations to a QML module and place them inside the module rather than at the root of the resource file system (something like a TRANSLATIONS argument to qt_add_qml_module or a separate qt_add_qml_translations function).
• Provide an API to configure the expected location(s) and prefixes of *.qm files (probably not necessary, though)

Side note

https://doc.qt.io/qt-6/qtranslator.html uses the word "prefix" a bit differently: For "qml_", "qml" is the filename while "_" is the prefix. Worth considering when we update our docs.