KF6 port: rework of plugin id adaption commits
Forked off from "work/igor/kf6" branch at the very commit "Make sure plugin names match the plugin Id", reworking only that, not readding other commits (left for your commits juggling, @igorkushnir :) ). For that reason sadly also untested, due to limited resources (see also section after list below).
First commit contains all changes to the CMake buildsystem (logical targets) to make the plugin binaries match the plugin ids. Also:
- squashed the fix-up commit
- added the qmljs plugin for completeness
- extended the commit message to be more verbose.
- changed for the scratchpad plugin, which has had an id without "kdev" prefix, to not change the id, but instead the plugin target/output name
The commit should be also apply-able for master, does not depend on anything Qt6/KF6. It only will result in some plugin binaries renamed. Will test next locally (update: -> !600 (merged))
The remaining commits in this MR contain the other changes found in the original commit, separated by aspect. See commit messages for comments/opinions on what to do with them perhaps.