This changes the Switch node so that it is implemented directly as a lazy-function,
instead of as a normal geometry node which uses `GeoNodeExecParams`. This improves
the design of the layered execution api, where different nodes can be implemented
at a proper different abstraction level. The simplest kinds of nodes are implemented
as multi-function, then there is `GeoNodeExecParams` and more specialized nodes are
implemented as lazy-function. The switch node is special in the sense that it currently
needs extra behavior in the lazy-function graph generation anyway.
`GeoNodeExecParams` can be simplified as well, because the Switch node was the only
one that used the `lazy_` methods.
We could consider adding back lazy-input functionality to normal geometry nodes
as it becomes necessary. Ideally, that could be integrated with the node declaration.
Pull Request: https://projects.blender.org/blender/blender/pulls/105696
258678916f