[turbofan] Refactor the lowering of element/property accesses.

src/field-index.h

Index: src/field-index.h
diff --git a/src/field-index.h b/src/field-index.h
index d0ae2f27f9c7ba4ea391f2d779181ebfc3577594..13bb94be41af151ae30f887189b882cbbbd768a7 100644
--- a/src/field-index.h
+++ b/src/field-index.h
@@ -76,6 +76,11 @@ class FieldIndex final {
         (IsInObjectBits::kMask | IsDoubleBits::kMask | IndexBits::kMask);
   }
 
+  bool operator==(FieldIndex const& other) const {
+    return bit_field_ == other.bit_field_;
+  }
+  bool operator!=(FieldIndex const& other) const { return !(*this == other); }
+
   // For GetLoadByFieldOffset.
   class FieldOffsetIsInobject : public BitField<bool, 1, 1> {};
   class FieldOffsetIsDouble : public BitField<bool, 2, 1> {};