Expose ddcCiAllowed accessors and ddcCi capability for Wayland

Jakob Petsovitsrequested to merge
work/jpetso/ddc-ci-allowed into master

Companion MR for libraries/plasma-wayland-protocols!98 (merged) and related MRs linked from there.

Requires an update to plasma-wayland-protocols.

In X11, this is a no-op.

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