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

model/Frame.h

@@ -52,6 +52,7 @@ namespace glabels
 			Frame( const Frame& other );
 
 		public:
+			virtual ~Frame();
 			virtual Frame* dup() const = 0;
 
 			QString id() const;