Replace early_error and sess.err with bug!, in all cases. If the
compiler we're running with, including plugins, is registering something
twice, that's a (compiler/plugin) programmer error -- we should not try
to be nice at the cost of developer ergononomics (hiding the stacktrace
of the second registration is bad).

This also is basically a static bug in ~all cases so it should not be a
detriment to users, including with plugins.

This is straight up removing dead code, but is a separate commit from
the previous to avoid conflating clean up and important changes.

This extracts the call to get_lints() to callers.

This is in preparation for on-demand constructing passes

This moves from calling get_lints on instantiated pass objects to the
raw object

This stops storing the pass objects and instead stores constructor
functions.

The primary effect is that LintStore no longer has any interior
mutability.

Moves this information to a direct field of Lint, which is where it
belongs.

Avoid querying LintStore when not necessary

Access through tcx is fine -- by that point, the lint store is frozen,
but direct access through Session will go away in future commits, as
lint store is still mutable in early stages of Session, and will be
removed completely.

Remove lint store from Session

Move to using Box<dyn Fn() -> ...> so that we can let plugins register
state.

This also adds a callback that'll get called from plugin registration so
that Clippy and other tools can register lints without using the plugin
API. The plugin API still works, but this new API is more compatible
with drivers other than rustc.