rustc_mir_dataflow: Add exports for external tools

Added back previously available exports:

* Forward/Backward: used when implementing `AnalysisDomain`
* Engine: used in user's code to solve the dataflow problem
* SwitchIntEdgeEffects: used when implementing functions of the `Analysis` trait
* graphviz: potentially useful for debugging purposes

These exports are used when implementing external tools based on MIR
dataflow framework.

Closes rust-lang#120130

Author: jubnzv

compiler/rustc_mir_dataflow/src/lib.rs

@@ -21,10 +21,10 @@ pub use self::drop_flag_effects::{
     move_path_children_matching, on_all_children_bits, on_lookup_result_bits,
 };
 pub use self::framework::{
-    fmt, lattice, visit_results, Analysis, AnalysisDomain, Direction, GenKill, GenKillAnalysis,
-    JoinSemiLattice, MaybeReachable, Results, ResultsCursor, ResultsVisitable, ResultsVisitor,
+    fmt, graphviz, lattice, visit_results, Analysis, AnalysisDomain, Backward, Direction, Engine,
+    Forward, GenKill, GenKillAnalysis, JoinSemiLattice, MaybeReachable, Results, ResultsCursor,
+    ResultsVisitable, ResultsVisitor, SwitchIntEdgeEffects,
 };
-use self::framework::{Backward, SwitchIntEdgeEffects};
 use self::move_paths::MoveData;
 
 pub mod debuginfo;