Update to Qt6

- New baseline minimum platform is Ubuntu 22.04
    - Qt6 requires at least 6.2
        - some deprecations may be flagged on later versions (e.g. 6.8)
    - CMake requires at least 3.22
- Include build-tests.yml github action to validate builds on mulitple platforms
- QtTest is no longer optional since it easily comes along for the ride with Qt
- Replaced QStringRef in model::SubstitutionField with simple ParserState class
- Removed deprecations up to Qt 6.2

glabels/main.cpp

@@ -51,7 +51,7 @@ int main( int argc, char **argv )
 	// Setup translators
 	//
 	QLocale locale = QLocale::system();
-	QString qtTranslationsDir = QLibraryInfo::location( QLibraryInfo::TranslationsPath );
+	QString qtTranslationsDir = QLibraryInfo::path( QLibraryInfo::TranslationsPath );
 	QString myTranslationsDir = glabels::model::FileUtil::translationsDir().canonicalPath();
 	
 	QTranslator qtTranslator;