Turn built-in effects into a library kwin links against

As all effects have always been compiled into the same .so file it's
questionable whether resolving the effects through a library is useful
at all. By linking against the built-in effects we gain the following
advantages:
* don't have to load/unload the KLibrary
* don't have to resolve the create, supported and enabled functions
* no version check required
* no dependency resolving (effects don't use it)
* remove the KWIN_EFFECT macros from the effects

All the effects are now registered in an effects_builtins file which
maps the name to a factory method and supported or enabled by default
methods.

During loading the effects we first check whether there is a built-in
effect by the given name and make a shortcut to create it through that.
If that's not possible the normal plugin loading is used.

Completely unscientific testing [1] showed an improvement of almost 10
msec during loading all the effects I use.

[1] QElapsedTimer around the loading code, start kwin five times, take
average.

REVIEW: 115073