Rollup merge of #66456 - Centril:driver-codes, r=Mark-Simulacrum

Move `DIAGNOSTICS` usage to `rustc_driver`

Remove `rustc_interface`'s dependency on `rustc_error_codes` and centralize all usages of `DIAGNOSTICS` in `rustc_driver`. Once we remove all references to `rustc_error_codes` in all other crates but `rustc_driver`, this should allow for incremental recompilation of the compiler to be smoother when tweaking error codes. This works towards https://github.com/rust-lang/rust/issues/66210#issuecomment-551862528.

(May include traces of minor drive-by cleanup.)

r? @Mark-Simulacrum

src/librustdoc/core.rs

@@ -21,7 +21,6 @@ use syntax::feature_gate::UnstableFeatures;
 use errors::json::JsonEmitter;
 use syntax::symbol::sym;
 use syntax_pos::DUMMY_SP;
-use errors;
 use errors::emitter::{Emitter, EmitterWriter};
 
 use std::cell::RefCell;
@@ -341,6 +340,7 @@ pub fn run_core(options: RustdocOptions) -> (clean::Crate, RenderInfo, RenderOpt
         lint_caps,
         register_lints: None,
         override_queries: None,
+        registry: rustc_driver::diagnostics_registry(),
     };
 
     interface::run_compiler_in_existing_thread_pool(config, |compiler| {