Add more APIs into std_specs

[hiroki-chen]

This PR does three things:

1. Implement ExDefault indicated in Support for Default::default(); #1951.
2. Implement slice APIs:

• Sorted-related: binary_search_*, is_sorted_.
• Slice manipulations reverse, rotate_, swap, etc.
• Misc: contains, starts_with, ends_with, etc.

3. Move unreachable_unchecked into the correct place control_flow.

By submitting this pull request, I confirm that my contribution is made under the terms of the MIT license.

[sssxks]

hi, i am currently blocked by Default::default() in my verus project. your pr contains ExDefault, but are you planning to finish it? i am happy to help by splitting a smaller PR containing only default.

[hiroki-chen]

hi, i am currently blocked by Default::default() in my verus project. your pr contains ExDefault, but are you planning to finish it? i am happy to help by splitting a smaller PR containing only default.

Thanks, you may cherry pick my draft PRs if needed, this is still a WIP one.