Build: qt6 build issues

[slspencer]

With Qt 6.2, MSVC 2019, and Qt Creator 10.01 on Windows 10 64-bit (Desktop_Qt_6_2_4_MSVC2019_64bit) The following issues appear during compiling:

• seamly2d\src\libs\vmisc\vabstractapplication.cpp:283: warning: C4834: discarding return value of function with 'nodiscard' attribute
• seamly2d\src\libs\vmisc\vabstractapplication.cpp:284: warning: C4834: discarding return value of function with 'nodiscard' attribute
• seamly2d\src\libs\vmisc\vabstractapplication.cpp:285: warning: C4834: discarding return value of function with 'nodiscard' attribute
• seamly2d\src\libs\vmisc\vabstractapplication.cpp:292: warning: C4834: discarding return value of function with 'nodiscard' attribute
• seamly2d\src\libs\vmisc\vabstractapplication.cpp:293: warning: C4834: discarding return value of function with 'nodiscard' attribute
• seamly2d\src\app\seamly2d\dialogs\export_layout_dialog.cpp:766: warning: C4003: not enough arguments for function-like macro invocation 'QStringLiteral'
• seamly2d\src\app\seamly2d\dialogs\export_layout_dialog.cpp:766: warning: C4003: not enough arguments for function-like macro invocation 'QT_UNICODE_LITERAL'
• seamly2d\src\app\seamly2d\dialogs\export_layout_dialog.cpp:88: warning: Definition of implicit copy constructor for 'QException' is deprecated because it has a user-provided destructor
• seamly2d\src\app\seamly2d\dialogs\export_layout_dialog.cpp:88: In implicit copy constructor for 'QException' first required here
• seamly2d\src\app\seamly2d\dialogs\export_layout_dialog.cpp:782: warning: Default label in switch which covers all enumeration values
• seamly2d\src\app\seamly2d\dialogs\export_layout_dialog.cpp:34: warning: Included header options.h is not used directly (fix available)