Provide means for containers where newly allocated elements of
trivially-constructible types are left uninitialized:

* `UninitializedAllocator`
* `UninitializedVector`, which is `std::vector` with `UninitializedAllocator`
* `UninitializedInlinedVector`, which is `absl::InlinedVector` with
  `UninitializedAllocator`

Add `VectorWriter` for `std::vector` including `UninitializedVector`,
`absl::InlinedVector` including `UninitializedInlinedVector`, and similar types.
Like `CompactStringWriter`, `VectorWriter` can be more efficient than
`StringWriter` when the destination can be resized with uninitialized space.

`VectorResizableTraits` is generalized from `std::vector` to similar types.
The template parameter is the whole vector type rather than the element type
and the allocator separately.

PiperOrigin-RevId: 866537234