This allows registering arbitrary objects on the core's registry and
finding them later, without having to add API for each and every object.
I think this is useful enough to have it public, even though it's
probably not going to be used that much... The rationale here is to
allow registering custom component loaders without having to make them
subclass WpPlugin or to create custom API for registering component
loaders specifically.
Also, remove the wp_plugin_register() and wp_si_factory_register()
functions, since they are not going to be used much in the future.
The idea is to let the component loader do the registration under the
scenes, as the component is getting loaded.
Aim for 8 pointers on each struct, wich exceptions:
- 12 pointers for already crowded/important ones
- 4 pointers for empty ones that are used for proxies; we are
unlikely to add any virtual methods on these classes ever
This adds WP_SESSION_ITEM_FEATURE_ACTIVE and WP_SESSION_ITEM_FEATURE_EXPORTED
features, so _activate and _export APIs have been removed. Modules and unit
tests have also been updated.
