Rollup merge of #140234 - nnethercote:separate-Analysis-and-Results, r=davidtwco

Separate dataflow analysis and results

`Analysis` gets put into `Results` with `EntryStates`, by `iterate_to_fixpoint`. This has two problems:
- `Results` is passed various places where only `Analysis` is needed.
- `EntryStates` is passed around mutably everywhere even though it is immutable.

This commit mostly separates `Analysis` from `Results` and fixes these two problems.

r? `@davidtwco`

Author: GuillaumeGomez

src/mir/dataflow.md

@@ -148,8 +148,7 @@ whereas this code uses [`ResultsCursor`]:
 
 ```rust,ignore
 let mut results = MyAnalysis::new()
-    .into_engine(tcx, body, def_id)
-    .iterate_to_fixpoint()
+    .iterate_to_fixpoint(tcx, body, None);
     .into_results_cursor(body);
 
 // Inspect the fixpoint state immediately before each `Drop` terminator.