[datapipe] Refactor datapipe execution. JB#22475

The datapipe_exec_xxx() helpers use O(N^2) implementation for O(N) task.
While the extra effort helps to avoid crashing if callbacks should be
removed during list traversal, it can still skip notifications if new
callbacks are registered.

Handle callback removal via invalidate immediately, garbage collect
later -mechanism. Inline helper functions to datapipe_exec_full()
and utilize O(N) list traversal.

Signed-off-by: Simo Piiroinen <simo.piiroinen@jollamobile.com>