strace: Improvements

- Added some utility functions to the `Context` class.
- Updated the `sockaddr` handler to retrieve the next sibling
rather than the sibling at index 2. This allows the handler to
work for syscalls where the `socklen_t` argument is not the third
one, for example, `_kern_recvfrom`.
- Added the ability to print the `flatArgs` for `_kern_exec` and
`_kern_load_image`.

Change-Id: Ia4cf0a30a5cf972274820bbf068101450db52189
Reviewed-on: https://review.haiku-os.org/c/haiku/+/6498
Reviewed-by: waddlesplash <waddlesplash@gmail.com>