This commit adds a new template hook exploreSketch() that allows plugins to efficiently
obtain compile-time known information about the sketch.
The hook is called before setup and is passed a _Sketch
template parameter that wraps two more types Plugins and StaticKeymap, whose static constexpr methods can be used
to explore the registered plugins and the static keymap.
Signed-off-by: Florian Fleissner <florian.fleissner@inpartik.de>