adding simplifiers layer

simplifiers layer is a common substrate for global non-incremental and incremental processing.
The first two layers are new, but others are to be ported form tactics.

- bv::slice - rewrites equations to cut-dice-slice bit-vector extractions until they align. It creates opportunities for rewriting portions of bit-vectors to common sub-expressions, including values.
- euf::completion - generalizes the KB simplifcation from asserted formulas to use the E-graph to establish a global and order-independent canonization.

The interface dependent_expr_simplifier is amenable to forming tactics. Plugins for asserted-formulas is also possible but not yet realized.

src/ast/simplifiers/bv_slice.h

@@ -0,0 +1,55 @@
+/*++
+Copyright (c) 2022 Microsoft Corporation
+
+Module Name:
+
+    bv_slice.h
+
+Abstract:
+
+    simplifier for extracting bit-vector ranges
+    It rewrites a state using bit-vector slices. 
+    Slices are extracted from bit-vector equality assertions 
+    in the style of (but not fully implementing a full slicing) 
+    Bjorner & Pichora, TACAS 1998 and Brutomesso et al 2008.
+
+Author:
+
+    Nikolaj Bjorner (nbjorner) 2022-11-2.
+
+--*/
+
+
+#pragma once
+
+#include "util/uint_set.h"
+#include "ast/bv_decl_plugin.h"
+#include "ast/simplifiers/dependent_expr_state.h"
+#include "ast/rewriter/th_rewriter.h"
+
+
+namespace bv {
+
+    class slice : public dependent_expr_simplifier {
+        bv_util                 m_bv;
+        th_rewriter             m_rewriter;
+        obj_map<expr, uint_set> m_boundaries;
+        ptr_vector<expr>        m_xs, m_ys;
+        
+        expr* mk_extract(unsigned hi, unsigned lo, expr* x);
+        void process_eqs();
+        void process_eq(expr* e);
+        void slice_eq();
+        void register_slice(unsigned lo, unsigned hi, expr* x);     
+        void apply_subst();
+        void get_concats(expr* x, ptr_vector<expr>& xs);
+        
+    public:
+
+        slice(ast_manager& m, dependent_expr_state& fmls) : dependent_expr_simplifier(m, fmls), m_bv(m), m_rewriter(m) {}
+
+        void push() override { dependent_expr_simplifier::push(); }
+        void pop(unsigned n) override { dependent_expr_simplifier::pop(n); }
+        void reduce() override;
+    };
+}