Rollup merge of #98930 - tmiasko:pub-basic-blocks, r=oli-obk

Make MIR basic blocks field public

This makes it possible to mutably borrow different fields of the MIR
body without resorting to methods like `basic_blocks_local_decls_mut_and_var_debug_info`.

To preserve validity of control flow graph caches in the presence of
modifications, a new struct `BasicBlocks` wraps together basic blocks
and control flow graph caches.

The `BasicBlocks` dereferences to `IndexVec<BasicBlock, BasicBlockData>`.
On the other hand a mutable access requires explicit `as_mut()` call.

clippy_lints/src/redundant_clone.rs

@@ -161,7 +161,7 @@ fn check_fn(
                 // `arg` is a reference as it is `.deref()`ed in the previous block.
                 // Look into the predecessor block and find out the source of deref.
 
-                let ps = &mir.predecessors()[bb];
+                let ps = &mir.basic_blocks.predecessors()[bb];
                 if ps.len() != 1 {
                     continue;
                 }