Virtual Keyboard should be prebuilt for all languages

From qtvirtualkeyboard/src/config.pri:

# Default language
!contains(CONFIG, lang-.*) {
    contains(QT_CONFIG, private_tests) { # CI or developer build, use all languages
        CONFIG += lang-all
    } else {
        CONFIG += lang-en_GB
    }
}

I would suggest to change this in the following way:

• always build with lang-all
• Set VirtualKeyboardSettings.activeLocales to only lang-en_GB as a default (Currently, both activeLocales and availableLocales in VirtualKeyboardSettings are empty by default)

In the result, the default behavior of Qt would just be the same: It would only show the English keyboard per default. However, this would make it possible for users of non-english keyboards to just use prebuilt Qt versions, without the need to rebuild the module.

I believe only building for English is a relic coming from earlier versions, where VirtualKeyboardSettings was not available yet: In these times, one had to build it that way to limit the available input languages.