Rollup merge of #120342 - oli-obk:track_errors6, r=nnethercote

Remove various `has_errors` or `err_count` uses

follow up to #119895

r? `@nnethercote` since you recently did something similar.

There are so many more of these, but I wanted to get a PR out instead of growing the commit list indefinitely. The commits all work on their own and can be reviewed commit by commit.

clippy_lints/src/transmute/utils.rs

@@ -37,12 +37,6 @@ pub(super) fn check_cast<'tcx>(
     let inherited = Inherited::new(cx.tcx, local_def_id);
     let fn_ctxt = FnCtxt::new(&inherited, cx.param_env, local_def_id);
 
-    // If we already have errors, we can't be sure we can pointer cast.
-    assert!(
-        !fn_ctxt.errors_reported_since_creation(),
-        "Newly created FnCtxt contained errors"
-    );
-
     if let Ok(check) = cast::CastCheck::new(
         &fn_ctxt,
         e,
@@ -53,17 +47,7 @@ pub(super) fn check_cast<'tcx>(
         DUMMY_SP,
         hir::Constness::NotConst,
     ) {
-        let res = check.do_check(&fn_ctxt);
-
-        // do_check's documentation says that it might return Ok and create
-        // errors in the fcx instead of returning Err in some cases. Those cases
-        // should be filtered out before getting here.
-        assert!(
-            !fn_ctxt.errors_reported_since_creation(),
-            "`fn_ctxt` contained errors after cast check!"
-        );
-
-        res.ok()
+        check.do_check(&fn_ctxt).ok()
     } else {
         None
     }