Complement the `struct k_mutex` in each fdtable entry
with a `struct k_condvar`. The reasoning for this should be
self-evident.
For a bit of history, `fdtable` was introduced in
commit 06eb489c45 ("kernel: add condition variables")
which predates `struct k_condvar`, introduced in
commit f484bbaa26 ("lib: posix: Implement generic file descriptor table")
by almost 2 years.
Additionally, provide a new accessor function,
`z_get_obj_lock_and_cond()`, that (optionally) gets the mutex
and condition variable associated with the provided object and
vtable.
Signed-off-by: Christopher Friedt <cfriedt@meta.com>
0014dd05f0