The dragstart does not propagate from shadow dom

[qwiglydee]

The created 'dragstart' event misses 'composed' flag set.

"""
The read-only composed property of the interface returns a boolean value which indicates whether or not the event will propagate across the shadow DOM boundary into the standard DOM.

All UA-dispatched UI events are composed (click/touch/mouseover/copy/paste, etc.).
Most other types of events are not composed, and so will return false.
"""

Use case: a custom element with lots of draggables in its shadow dom and a common ondragstart handler on itself.