Only send OutputConfig sendApplied / sendFailed to the right resource

Summary:
I don't understand the original logic.
s_allResources contains /every/ resource, not just outputconfigurations.

Sending org_kde_kwin_outputconfiguration_send_applied to a wl_surface (for example),
results in an error.

The reason kwin doesn't currently crash is because we don't actually send
applied/failed after setting outputs. (which is another bug)

Test Plan: The existing unit test still passes.

Reviewers: #plasma, sebas

Reviewed By: #plasma, sebas

Subscribers: sebas, plasma-devel, #frameworks

Tags: #plasma_on_wayland, #frameworks

Differential Revision: https://phabricator.kde.org/D7898