MSVC compiler warnings stemming from Qt header files

Issue type

Other type of issue

Description with steps to reproduce

When building MuseScore Studio using MSVC, there show very many compiler warnings reg. "unreachable code" (C4702), all stemming from 3 Qt header files, qvariant.h (77 warnings), qjsengine.h (389 warnings) and qjsprimitivevalue.h (22 warnings).

Besides being just annoying they can also cause missing the tree in the forrest, the valid compiler warning in code we own and control and want to knoe about and react upon.
Also this prevents the use of compiler options that causes warnings to be treated as errors (MSVC: /WX, gcc: -Werror), which would be usefull esp. on GitHub CI

Supporting files, videos and screenshots

n/a

In which versions of MuseScore Studio is this issue present?

all versions

Regression

Yes, this used to work in MuseScore 3.x and now is broken
To be fair: Mu3 used a different (older) Qt version...

Operating system

Windows 11

Additional context

n/a

Checklist

• This report follows the guidelines for reporting bugs and issues
• I have verified that this issue has not been logged before, by searching the issue tracker for similar issues
• I have attached all requested files and information to this report
• I have attempted to identify the root problem as concisely as possible, and have used minimal reproducible examples where possible

Reproduce the Windows 11 MSVC build and record the C4702 warnings from qvariant.h, qjsengine.h, and qjsprimitivevalue.h. Start by inspecting how Qt headers and compiler warning options are configured in the build, then compare the current behavior with MuseScore 3.x if available. Done means these third-party warnings no longer obscure project warnings and warning-as-error options can be used as intended.