Rollup merge of #76775 - ecstatic-morse:dataflow-extra-tab-diff, r=Mark-Simulacrum

Strip a single leading tab when rendering dataflow diffs

The `fmt_diff_with` formatter uses a tab to separate additions from subtractions. Strip it when rendering those diffs on separate lines.

r? @Mark-Simulacrum (since you're speedy)

compiler/rustc_mir/src/dataflow/framework/graphviz.rs

@@ -578,7 +578,7 @@ fn diff_pretty<T, C>(new: T, old: T, ctxt: &C) -> String
         return String::new();
     }
 
-    let re = Regex::new("\u{001f}([+-])").unwrap();
+    let re = Regex::new("\t?\u{001f}([+-])").unwrap();
 
     let raw_diff = format!("{:#?}", DebugDiffWithAdapter { new, old, ctxt });