Add #[track_caller] to bug! and register_renamed

Before:

```
thread 'rustc' panicked at 'compiler/rustc_lint/src/context.rs:267:18: invalid lint renaming of broken_intra_doc_links to rustdoc::broken_intra_doc_links', compiler/rustc_middle/src/util/bug.rs:34:26
```

After:

```
thread 'rustc' panicked at 'src/librustdoc/core.rs:455:24: invalid lint renaming of broken_intra_doc_links to rustdoc::broken_intra_doc_links', compiler/rustc_middle/src/util/bug.rs:35:26
```

The reason I added it to `register_renamed` too is that any panic in
that function will be the caller's fault.

compiler/rustc_lint/src/context.rs

@@ -261,6 +261,7 @@ impl LintStore {
         }
     }
 
+    #[track_caller]
     pub fn register_renamed(&mut self, old_name: &str, new_name: &str) {
         let target = match self.by_name.get(new_name) {
             Some(&Id(lint_id)) => lint_id,

compiler/rustc_middle/src/util/bug.rs

@@ -21,6 +21,7 @@ pub fn span_bug_fmt<S: Into<MultiSpan>>(span: S, args: fmt::Arguments<'_>) -> !
     opt_span_bug_fmt(Some(span), args, Location::caller());
 }
 
+#[track_caller]
 fn opt_span_bug_fmt<S: Into<MultiSpan>>(
     span: Option<S>,
     args: fmt::Arguments<'_>,