There are no advantages for the effects KCM to have all the effect
config modules in one plugin.
By having a plugin per effect we can use the KPluginTrader to easily
find the configuration plugin for a given effect and load it.
To make this possible the following changes are done:
* config_builtins.cpp is deleted
* add_subdirectory is used for all effects which have a config module
* toplevel CMakeLists.txt contains the sources again for the effects
which have a config module, but effects which don't have a config
module are still included and thus the macro is still used
* plugin created for the config module, name pattern is:
kwin_effectname_config
* plugin installed to ${PLUGIN_INSTALL_DIR}/kwin/effects/configs
* desktop file adjusted to new plugin name and keyword removed
* desktop file converted to json as meta data and no longer installed
* Uses K_PLUGIN_FACTORY_WITH_JSON
* Macros for config are dropped from kwineffects.h
REVIEW: 116854
