posix: deprecate PTHREAD_IPC _MUTEX _COND and _KEY

Zephyr's POSIX API is moving toward using the standard
nomenclature from IEEE 1003.1-2017 for as much as possible. In
particular, we want to have consistent naming between Zephyr's
POSIX API Kconfig options and the naming for POSIX Options and
Option Groups.

The Kconfig option CONFIG_PTHREAD_IPC has been (ab)used for a
very long time for a variety of different purposes. However,
the standard Option / feature test macro for POSIX Threads is,
intuitively _POSIX_THREADS. There is a corresponding sysconf()
key named _SC_POSIX_THREADS.

Annoyingly, the POSIX Option Group that corresponds to the
Option is POSIX_THREADS_BASE, which is a minor inconsistency
in the standard.

The _POSIX_THREADS Option already includes mutexes, condition
variables, and thread-specific storage (keys). So with this
change, we also deprecate the redundant Kconfig variables that
do not have a corresponding match in the standard.

- CONFIG_PTHREAD_IPC
- CONFIG_PTHREAD
- CONFIG_PTHREAD_COND
- CONFIG_PTHREAD_MUTEX
- CONFIG_PTHREAD_KEY

Additionally, create Kconfig variables for those configurables
which we are lacking:

- CONFIG_POSIX_THREADS_EXT
- CONFIG_POSIX_THREAD_ATTR_STACKSIZE
- CONFIG_POSIX_THREAD_ATTR_STACKADDR
- CONFIG_POSIX_THREAD_PRIORITY_SCHEDULING
- CONFIG_POSIX_THREAD_PRIO_INHERIT
- CONFIG_POSIX_THREAD_PRIO_PROTECT
- CONFIG_POSIX_THREAD_SAFE_FUNCTIONS

Some Kconfig variables were renamed to more properly match the spec:

- CONFIG_MAX_PTHREAD_COUNT -> CONFIG_POSIX_THREAD_THREADS_MAX
- CONFIG_MAX_PTHREAD_KEY_COUNT -> CONFIG_POSIX_THREAD_KEYS_MAX

Signed-off-by: Chris Friedt <cfriedt@tenstorrent.com>