Add zsh completions (compdef) for kscreen-doctor

Top-notch context-aware completions for kscreen-doctor with fine-grained
tags, descriptions and dynamic selection of outputs and their available
modes. In the output completion menu it displays status of outputs and
sorts enabled ones first. In the modes selection it brings current mode
to the top (if any), then lists output's preferred ones, all marked
accordingly, and finally dumps all other available modes. All modes are
pretty-formatted to be nicely aligned and easily distinguishable while
inserting correct compact mode ID upon completion.

Note: it uses the new variable KDE_INSTALL_ZSHAUTOCOMPLETEDIR, which was
added in ECM 5.101.

Read more: frameworks/extra-cmake-modules!310