[kwin] Add isEffectSupported method to Effects DBus interface

EffectsHandlerImpl::isEffectsSupported performs the check whether the
effect with the given name is supported by the current compositor.

The check is the following:
* if effect is already loaded, it is supported
* if the effect cannot be found, it is not supported
* if it's a scripted effect, it's always supported
* if it's a built-in effect, we ask BuiltInEffects::supported
* for all other effects we resolve the library and the supported
method

The idea behind providing this functionality in the DBus interface is
to allow filtering in the effects KCM for the effects which are
supported by the current compositor.

In addition a areEffectsSupported method is added which takes a
list of names and returns a list of bools.

REVIEW: 116665