[libc] Migrate from baremetal stdio.h to generic stdio.h (#152748)

This is a follow up to the RFC here:

https://discourse.llvm.org/t/rfc-implementation-of-stdio-on-baremetal/86944

This provides the stdout/stderr/stdin symbols (which now don't have to
provided by the user). This allows the user to have access to all
functions, currently I've only tested `fprintf` but in theory everything
that works in the generic folder should work in the baremetal
configuration.

All streams are _non-buffered_, which does NOT require flushing. It is
based on the CookieFile that already existed

GitOrigin-RevId: 020dff4be832e035a24fcdb13e26d7c2e69887eb