Add TF_LoadPluggableDeviceLibrary API #381

Although TF_LoadPluggableDeviceLibrary is an experimental API, it is necessary to use GPU on platform like Mac Arm.

I tried to include this API in code generating but it caused other errors.
Now I always add it manually.

extern "C" {
    pub fn TF_LoadPluggableDeviceLibrary(
        library_filename: *const ::std::os::raw::c_char,
        status: *mut TF_Status,
    ) -> *mut TF_Library;
}

This API had better be included.