py/emitnative: Implement yield and yield-from in native emitter.

This commit adds first class support for yield and yield-from in the native
emitter, including send and throw support, and yields enclosed in exception
handlers (which requires pulling down the NLR stack before yielding, then
rebuilding it when resuming).

This has been fully tested and is working on unix x86 and x86-64, and
stm32.  Also basic tests have been done with the esp8266 port.  Performance
of existing native code is unchanged.

py/objfun.c

@@ -154,7 +154,7 @@ STATIC const mp_obj_type_t mp_type_fun_native;
 qstr mp_obj_fun_get_name(mp_const_obj_t fun_in) {
     const mp_obj_fun_bc_t *fun = MP_OBJ_TO_PTR(fun_in);
     #if MICROPY_EMIT_NATIVE
-    if (fun->base.type == &mp_type_fun_native) {
+    if (fun->base.type == &mp_type_fun_native || fun->base.type == &mp_type_native_gen_wrap) {
         // TODO native functions don't have name stored
         return MP_QSTR_;
     }