Aslp generating control flow branches

[katrinafyi]

ensures a pc increment on all straight-line control-flow paths by construction.

adds a new lib/transforms/aslp/aslp_lexpr.ml file for abstracting the builtin and local variables used by the aslp lifter.

this pr also renames some things, like now using aslp_diamond in place of aslp_state.

let%expect_test "lift: b.eq #1024" =
  let module I = (val Bincaml_ibi.from_generator (Aslp_state.empty_aslp_ids ()))
  in
  let x =
    lift_opcode
      (module I)
      ~address:(Bitvec.zero ~size:64)
      (Bitvec.of_string "0x54002000:bv32")
  in
  print_endline @@ Aslp_state.show_aslp_diamond x;
  [%expect
    {|
    { Aslp_state.blocks = "block_0"
      -> { Aslp_state.assume = None; stmts = []; succs = ["block_1"; "block_2"];
           has_pc_assign = false },
      "block_1"
      -> { Aslp_state.assume = (Some eq($PSTATE_Z, 0x1:bv1));
           stmts = [var BranchTaken:bool := true; $PC:bv64 := 0x400:bv64];
           succs = ["block_3"]; has_pc_assign = true },
      "block_2"
      -> { Aslp_state.assume = (Some boolnot(eq($PSTATE_Z, 0x1:bv1)));
           stmts =
           [($PC:bv64 := bvadd($PC, 0x4:bv32), var BranchTaken:bool := false)];
           succs = ["block_3"]; has_pc_assign = true },
      "block_3"
      -> { Aslp_state.assume = None; stmts = []; succs = []; has_pc_assign = true
           };
      entry = "block_0"; exit = "block_3" }
    |}]