[libc++][test] Improve tests for assign in std::vector and vector<bool> (#119163)

This PR enhances the test coverage for std::vector::assign by adding new
tests for several important test cases that were previously missing, as
shown in the following table:

| test cases                        | forward_iterator | input_iterator |
|-----------------------------------|------------------|----------------|
| new_size > capacity()             | Yes              | Yes            |
| size() < new_size <= capacity()   | No               | No             |
| new_size <= size()                | No               | No             |

Similarly, no tests have previously covered `assign(InputIterator, InputIterator)`
and `assign(size_type, const value_type&)` for `vector<bool>`.

With this patch applied, all missing tests are covered.

0 files changed, 0 insertions, 0 deletions