message: refactor: Lift prevector default vals to the member declaration
  This is a port of Core
diff: @@ -245,7 +245,7 @@ public:
  };
  private:
  - size_type _size;
  + size_type _size = 0;
  union direct_or_indirect {
  char direct[sizeof(T) * N];
  struct
  @@ -253,7 +253,7 @@ private:
  size_type capacity;
  char *indirect;
  };
  - } _union;
  + } _union = {};
  T *direct_ptr(difference_type pos) { return reinterpret_cast<T *>(_union.direct) + pos; }
  const T *direct_ptr(difference_type pos) const { return reinterpret_cast<const T *>(_union.direct) + pos; }
  @@ -356,9 +356,9 @@ public:
  fill(item_ptr(0), first, last);
  }
  - prevector() : _size(0), _union{{}} {}
  - explicit prevector(size_type n) : prevector() { resize(n); }
  - explicit prevector(size_type n, const T &val) : prevector()
  + prevector() {}
  + explicit prevector(size_type n) { resize(n); }
  + explicit prevector(size_type n, const T &val)
  {
  change_capacity(n);
  _size += n;
  @@ -366,7 +366,7 @@ public:
  }
  template <typename InputIterator>
  - prevector(InputIterator first, InputIterator last) : prevector()
  + prevector(InputIterator first, InputIterator last)
  {
  size_type n = last - first;
  change_capacity(n);
  @@ -374,7 +374,7 @@ public:
  fill(item_ptr(0), first, last);
  }
  - prevector(const prevector<N, T, Size, Diff> &other) : prevector()
  + prevector(const prevector<N, T, Size, Diff> &other)
  {
  size_type n = other.size();
  change_capacity(n);
  @@ -382,7 +382,7 @@ public:
  fill(item_ptr(0), other.begin(), other.end());
  }
  - prevector(prevector<N, T, Size, Diff> &&other) : prevector() { swap(other); }
  + prevector(prevector<N, T, Size, Diff> &&other) { swap(other); }
  prevector &operator=(const prevector<N, T, Size, Diff> &other)
  {
  if (&other == this)
  