Include what you need, don't rely on transitive
includes. Forward-declare what you need in-name-only.
Also port the one unchanged include in the header
(qabstracteventdispatcher.h) to idiomatic form. It's an unrelated
change, but it looked so lost among the QtCore/ headers, I felt pity.
Amends e0573e7364.
Change-Id: I4f25df7465f08378bc4e003bde12c28f4d231f14
Reviewed-by: Ahmad Samir <a.samirh78@gmail.com>
(cherry picked from commit 49d5b0a5a10634841122bbbc5e986ce307e7017a)
Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org>
dabfdb5f2d