ecore_wl2: Replace window ids with pointers

Summary:
There's no benefit to generating ids instead of just using the
Ecore_Wl2_Window pointer in events.

This has the added benefit of working around a really nasty hash collision
bug when multiple ecore_evas engines are used at once.

ref T7053
ref T6222

@beta_break
Depends on D6521

Reviewers: devilhorns

Reviewed By: devilhorns

Subscribers: cedric, committers, zmike

Tags: efl

Maniphest Tasks: T7053, T6222

Differential Revision: https://phab.enlightenment.org/D6522