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

glbarcode/BarcodeCode39Ext.cpp

@@ -80,7 +80,7 @@ namespace glbarcode
 	{
 		for (char c : rawData)
 		{
-			if ( (c < 0) || (c > 0x7F) )
+			if ( c < 0 )
 			{
 				return false;
 			}

glbarcode/CMakeLists.txt

@@ -42,5 +42,5 @@ target_include_directories (glbarcode
 )
 
 target_link_libraries (glbarcode
-  Qt5::Widgets
+  Qt6::Widgets
 )

glbarcode/Matrix.h

@@ -116,16 +116,7 @@ namespace glbarcode
 		/**
 		 * Indirection "[]" operator
 		 */
-		inline T* operator[]( int i )
-		{
-			return (mData + (mNx * i));
-		}
-
-
-		/**
-		 * Indirection "[]" operator
-		 */
-		inline T const*const operator[]( int i ) const
+		inline T* operator[]( int i ) const
 		{
 			return (mData + (mNx * i));
 		}

glbarcode/QtRenderer.cpp

@@ -134,7 +134,7 @@ namespace glbarcode
 			font.setPointSizeF( FONT_SCALE*size );
 
 			QFontMetricsF fm( font );
-			double xCorner = x - fm.width( QString::fromStdString(text) )/2.0;
+			double xCorner = x - fm.horizontalAdvance( QString::fromStdString(text) )/2.0;
 			double yCorner = y - fm.ascent();
 		
 			QTextLayout layout( QString::fromStdString(text), font );