This will probably need to get tweaked once the privacy rules have been fully
agreed on, but for now this has all of the infrastructure necessary for
filtering out private items.
Closes#9410
In doing so, also remove the collapse-privacy pass because it's a little
over-zealous and may not be right 100% of the time (not used right now as well)
This can cause unexpected errors in the runtime when done while
scheduler threads are still initializing. Required some restructuring
of the main_args functions in our libraries.
Removes old rustdoc, moves rustdoc_ng into its place instead (plus drops the _ng
suffix). Also shreds all reference to rustdoc_ng from the Makefile rules.
