Revert "Auto merge of #89709 - clemenswasser:apply_clippy_suggestions_2, r=petrochenkov"

The PR had some unforseen perf regressions that are not as easy to find.
Revert the PR for now.

This reverts commit 6ae8912a3e, reversing
changes made to 86d6d2b738.

compiler/rustc_index/src/bit_set.rs

@@ -990,8 +990,9 @@ impl<R: Idx, C: Idx> BitMatrix<R, C> {
     pub fn insert_all_into_row(&mut self, row: R) {
         assert!(row.index() < self.num_rows);
         let (start, end) = self.range(row);
-        for word in self.words[start..end].iter_mut() {
-            *word = !0;
+        let words = &mut self.words[..];
+        for index in start..end {
+            words[index] = !0;
         }
         self.clear_excess_bits(row);
     }
@@ -1143,7 +1144,7 @@ impl<R: Idx, C: Idx> SparseBitMatrix<R, C> {
 
     /// Iterates through all the columns set to true in a given row of
     /// the matrix.
-    pub fn iter(&self, row: R) -> impl Iterator<Item = C> + '_ {
+    pub fn iter<'a>(&'a self, row: R) -> impl Iterator<Item = C> + 'a {
         self.row(row).into_iter().flat_map(|r| r.iter())
     }