Static assertion failed with QVarLengthArray<std::vector<std::unique_ptr<int>>>

Starting from Qt 6.4.0,  using

 QVarLengthArray<std::vector<std::unique_ptr<int>>>

we hit an static assert in stl_uninitialized.h when using resize().

 
 /usr/include/c++/12.2.0/bits/stl_construct.h:115:28: error: no matching function for call to ‘construct_at(std::unique_ptr<AutoPanGroupState, std::default_delete<AutoPanGroupState> >*&, const std::unique_ptr<AutoPanGroupState, std::default_delete<AutoPanGroupState> >&)’
115 | std::construct_at(_p, std::forward<_Args>(_args)...);

This is a regression since https://github.com/qt/qtbase/commit/a00a1d8806cfbf17e04b88d1b4ff4a9cf5b6294a#diff-3f4287973382b16af82c02e80740e5efbb0e5753771a19d6309eb2f7f6f6cd6d

Because std::is_copy_constructible_v<T> is true in our case

https://github.com/qt/qtbase/blob/067b53864112c084587fa9a507eb4bde3d50a6e1/src/corelib/tools/qvarlengtharray.h#L752

see also https://godbolt.org/z/948xd73xT

I think that can be solved by moving the value constructing version of

reallocate_impl() into a new function and not use a nullptr to destinguish the cases.

The original Bug has been reported here:

https://github.com/mixxxdj/mixxx/issues/11167