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

cmake/Modules/FindGnuBarcode.cmake

@@ -36,6 +36,9 @@ endif ()
 if (GNUBARCODE_INCLUDE_DIR AND EXISTS "${GNUBARCODE_INCLUDE_DIR}/barcode.h")
   file (STRINGS "${GNUBARCODE_INCLUDE_DIR}/barcode.h" BARCODE_H REGEX "^#define BARCODE_VERSION *\"[^\"]*\"")
   string (REGEX REPLACE "^.*VERSION *\"([^\"]*)\"" "\\1" GNUBARCODE_VERSION_STRING "${BARCODE_H}")
+  if (NOT "${BARCODE_H}")
+    set(GNUBARCODE_VERSION_STRING "0.99")  # ubuntu v0.99 may have barcode.h, but no version string
+  endif()
 endif()
 
 # handle the QUIETLY and REQUIRED arguments and set GNUBARCODE_FOUND to TRUE if