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
The only users of `SERIO\FWID` and `I2C\NAME` are already 'safe' and
the device GUIDs should all be unchanged.
There are no current users of the `MTD\NAME` instance IDs, and these
are the ones that may be more unpredictable and in need of sanity.
We were calling g_module_symbol() 2703 times, which is actually more
expensive than you'd think.
It also means the plugins are actually what we tell people they are:
A set of vfuncs that get run. The reality before that they were dlsym'd
functions that get called at pretty random times.
