doctor: Add "activeOutput" as valid screen ID and HDR enhancements

Yossef Rostaqirequested to merge
yossef/libkscreen:doctor_active_output_hdr_enhancements into master

These works have been done to accommodate this change: kscreen!461

Instead of having to specify a screen ID for altering an output, we can use the keyword "activeOutput" to refer to the current active display.

Additionally, the "hdrAndWcg" sub command has been added to jointly be able to switch the two and ensure their states are coupled.

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