[#490] Enable loan_slice APIs in CXX bindings

[orecham]

Notes for Reviewer

1. Implement iox::Slice
2. Implement loan_slice APIs in C++ binding
3. Expose properties payload_alignment and max_slice_len in C++ binding

Pre-Review Checklist for the PR Author

1. Add sensible notes for the reviewer
2. PR title is short, expressive and meaningful
3. Relevant issues are linked in the References section
4. Every source code file has a copyright header with SPDX-License-Identifier: Apache-2.0 OR MIT
5. Branch follows the naming format (iox2-123-introduce-posix-ipc-example)
6. Commits messages are according to this guideline
   • Commit messages have the issue ID ([#123] Add posix ipc example)
   • Commit author matches Eclipse Contributor Agreement (and ECA is signed)
7. Tests follow the best practice for testing
8. Changelog updated in the unreleased section including API breaking changes
9. Assign PR to reviewer
10. All checks have passed (except task-list-completed)

Checklist for the PR Reviewer

• Commits are properly organized and messages are according to the guideline
• Unit tests have been written for new behavior
• Public API is documented
• PR title describes the changes

Post-review Checklist for the PR Author

1. All open points are addressed and tracked via issues

References

Closes #490

[elfenpiff]

I found another issue with the Slice I overlooked in the previous reviews. We need to introduce a ConstIterator so that the user does not change the const MutableSlice content by accident when they iterate over the slice elements.

[elfenpiff]

When the Rust example is adjusted we can merge it