This allows creating the silo when starting the engine with custom
plugin keys such as WacomI2cFlashBaseAddr.
If we move the plugin initialization earlier then we don't get the
HwID matches, so we really do have to split this into a 4-stage startup,
e.g. ->load(), ->init(), ->startup() and ->coldplug().
Some plugins were creating local versions (which were not attached to
the daemon progress in any way) as a workaround as they needed to do
actions that took a long time to complete.
Provide a device instance builder that allows plugins to easily
create multiple instance IDs based on parent attributes.
Also fix a lot of the instance ID orders, so that we add more generic
IDs first, and more specific IDs after.
tristate features will automatically disable if dependencies marked
as required are missing.
Packagers can manually override using `auto_features`.
Link: https://mesonbuild.com/Build-options.html#features
