[turbofan] Add SimplifiedOperator::Allocate operator.

src/compiler/access-builder.cc

Index: src/compiler/access-builder.cc
diff --git a/src/compiler/access-builder.cc b/src/compiler/access-builder.cc
index 1462c48f22348779ef4028eff20e0ad53df59aef..0b1769bc4af0b49df4abf6ca4267f2ab532e55ab 100644
--- a/src/compiler/access-builder.cc
+++ b/src/compiler/access-builder.cc
@@ -45,6 +45,13 @@ FieldAccess AccessBuilder::ForJSArrayBufferBackingStore() {
 
 
 // static
+FieldAccess AccessBuilder::ForFixedArrayLength() {
+  return {kTaggedBase, FixedArray::kLengthOffset, MaybeHandle<Name>(),
+          Type::TaggedSigned(), kMachAnyTagged};
+}
+
+
+// static
 FieldAccess AccessBuilder::ForExternalArrayPointer() {
   return {kTaggedBase, ExternalArray::kExternalPointerOffset,
           MaybeHandle<Name>(), Type::UntaggedPointer(), kMachPtr};