Fix crash with -Zdump-mir-dataflow

As of #133155 `Formatter:new` uses `as_results_cursor` to create a
non-mutable results reference, and then later that is accessed via
`deref_mut` which results in a runtime abort. Changing to
`as_results_cursor_mut` fixes it.

Fixes #133641.

Author: nnethercote

Diff for: compiler/rustc_mir_dataflow/src/framework/graphviz.rs

@@ -47,11 +47,11 @@ where
 {
     pub(crate) fn new(
         body: &'mir Body<'tcx>,
-        results: &'mir Results<'tcx, A>,
+        results: &'mir mut Results<'tcx, A>,
         style: OutputStyle,
     ) -> Self {
         let reachable = mir::traversal::reachable_as_bitset(body);
-        Formatter { cursor: results.as_results_cursor(body).into(), style, reachable }
+        Formatter { cursor: results.as_results_cursor_mut(body).into(), style, reachable }
     }
 
     fn body(&self) -> &'mir Body<'tcx> {

Diff for: compiler/rustc_mir_dataflow/src/framework/mod.rs

@@ -281,10 +281,10 @@ pub trait Analysis<'tcx> {
             );
         }
 
-        let results = Results { analysis: self, entry_sets };
+        let mut results = Results { analysis: self, entry_sets };
 
         if tcx.sess.opts.unstable_opts.dump_mir_dataflow {
-            let res = write_graphviz_results(tcx, body, &results, pass_name);
+            let res = write_graphviz_results(tcx, body, &mut results, pass_name);
             if let Err(e) = res {
                 error!("Failed to write graphviz dataflow results: {}", e);
             }

Diff for: compiler/rustc_mir_dataflow/src/framework/results.rs

@@ -95,7 +95,7 @@ where
 pub(super) fn write_graphviz_results<'tcx, A>(
     tcx: TyCtxt<'tcx>,
     body: &mir::Body<'tcx>,
-    results: &Results<'tcx, A>,
+    results: &mut Results<'tcx, A>,
     pass_name: Option<&'static str>,
 ) -> std::io::Result<()>
 where