rust: provide examples for C library generation in rust

rust: provide examples for C library generation in rust

rust-c-lib-example is a little rust code which provide
a single function to print a formatted date (via the chrono crate)
from an input timestamp in millisecond. It has the necessary FFI
annotation and inherit cargo_c class for the C ABI compatible
library generation.

rust-c-lib-example is meson project for the C code which
will call the print_date function from rust-c-lib-example
if no argument is provided, if any argument is provided
it will print "Hello world in rust from C!"

add a runtime test case to check if all went well.

Signed-off-by: Frederic Martinsons <frederic.martinsons@gmail.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>