[libc++] Slightly simplify max_size and add new tests for vector (#119990)

This PR slightly simplifies the implementation of `vector<bool>::max_size`
and adds extensive tests for the `max_size()` function for both `vector<bool>`
and `vector<T>`. The main purposes of the new tests include:

- Verify correctness of `max_size()` under various `size_type` and
  `difference_type` definitions: check that `max_size()` works properly
  with allocators that have custom `size_type` and `difference_type`. This
  is particularly useful for `vector<bool>`, as different `size_type` lead
  to different `__storage_type` of different word lengths, resulting in
  varying `max_size()` values for `vector<bool>`. Additionally, different
  `difference_type` also sets different upper limit of `max_size()` for
  both `vector<bool>` and `std::vector`. These tests were previously
  missing.

- Eliminate incorrect implementations: Special tests are added to identify and
  reject incorrect implementations of `vector<bool>::max_size` that unconditionally
  return `std::min<size_type>(size-max, __internal_cap_to_external(allocator-max-size))`.
  This can cause overflow in the `__internal_cap_to_external()` call and lead
  to incorrect results. The new tests ensure that such incorrect
  implementations are identified.

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