ecore: add promise for Ecore_Thread

ecore: add promise for Ecore_Thread

Add ecore_thread_promise_run function that returns a Promise
and runs function in another thread which you can set the
value on a Eina_Promise_Owner.

Eina_Promise* promise;
Ecore_Thread* thread = ecore_thread_promise_run
( &function_heavy, &cancellation_function, private_data,
sizeof(ValueType), &promise);

This calls function_heavy on another thread and returns
the Ecore_Thread and a Eina_Promise as an out-parameter.

Signed-off-by: Cedric Bail <cedric@osg.samsung.com>