Revert "Actually remove insert_bb"

This reverts commit 579f6e3.

kani-compiler/src/kani_middle/transform/body.rs

@@ -322,6 +322,31 @@ impl MutableBody {
         };
     }
 
+    /// Insert basic block before or after the source instruction and update `source` accordingly. If
+    /// `InsertPosition` is `InsertPosition::Before`, `source` will point to the same instruction as
+    /// before. If `InsertPosition` is `InsertPosition::After`, `source` will point to the
+    /// terminator of the newly inserted basic block.
+    pub fn insert_bb(
+        &mut self,
+        mut bb: BasicBlock,
+        source: &mut SourceInstruction,
+        position: InsertPosition,
+    ) {
+        // Splitting adds 1 block, so the added block index is len + 1;
+        let split_bb_idx = self.blocks().len();
+        let inserted_bb_idx = self.blocks().len() + 1;
+        // Update the terminator of the basic block to point at the remaining part of the split
+        // basic block.
+        let target = get_mut_target_ref(&mut bb.terminator);
+        *target = split_bb_idx;
+        let new_term = Terminator {
+            kind: TerminatorKind::Goto { target: inserted_bb_idx },
+            span: source.span(&self.blocks),
+        };
+        self.split_bb(source, position, new_term);
+        self.blocks.push(bb);
+    }
+
     pub fn insert_terminator(
         &mut self,
         source: &mut SourceInstruction,