`include-what-you-use` diagnostics, in practice, are specific to
the environment's compiler and standard library. Update includes
to satisfy IWYU for our CI job under Debian 12.
This allows collation to give a useful error message when it finds usage
of a private module rather than collation just not informing the
compilation and the compiler erroring out about not being able to import
unknown modules (which exists, but it was not told about due to
visibility).
Fixes: #24652
This structure allows representing whether a module is private in order
to give a more useful error message when its usage is attempted from
another target.
The call site already owns a path it doesn't need when the callback
returns. Hand ownership to the callback so it can optionally mutate
the path without necessarily allocating.
