[Interpreter] Preserve source positions in peephole optimizer.

test/cctest/interpreter/bytecode_expectations/BasicLoops.golden

 #
 # Autogenerated by generate-bytecode-expectations.
 #
 
 ---
 pool type: mixed
 execute: yes
 wrap: yes
 
 ---
 snippet: "
   var x = 0;
   while (false) { x = 99; break; continue; }
   return x;
 "
 frame size: 1
 parameter count: 1
-bytecode array length: 5
+bytecode array length: 6
 bytecodes: [
   /*   30 E> */ B(StackCheck),
   /*   42 S> */ B(LdaZero),
   /*   42 E> */ B(Star), R(0),
+  /*   88 S> */ B(Nop),
   /*   98 S> */ B(Return),
 ]
 constant pool: [
 ]
 handlers: [
 ]
 
 ---
 snippet: "
   var x = 0;
   while (false) {
     x = x + 1;
   };
   return x;
 "
 frame size: 1
 parameter count: 1
-bytecode array length: 5
+bytecode array length: 6
 bytecodes: [
   /*   30 E> */ B(StackCheck),
   /*   42 S> */ B(LdaZero),
   /*   42 E> */ B(Star), R(0),
+  /*   77 S> */ B(Nop),
   /*   87 S> */ B(Return),
 ]
 constant pool: [
 ]
 handlers: [
 ]
 
 ---
 snippet: "
   var x = 0;
@@ skipping 794 matching lines @@
 ]
 constant pool: [
   InstanceType::FIXED_ARRAY_TYPE,
   InstanceType::SHARED_FUNCTION_INFO_TYPE,
   InstanceType::ONE_BYTE_INTERNALIZED_STRING_TYPE,
   InstanceType::ONE_BYTE_INTERNALIZED_STRING_TYPE,
 ]
 handlers: [
 ]