[Intl] move strings for V8_INTL_SUPPORT.

Move strings in heap-symbols.h that only used inside V8_INTL_SUPPORT
under INTERNALIZED_STRING_LIST_GENERATOR_INTL so non intl users won't
use unnecessary memory. Also avoid two NewStringFromStaticChars calls
for string already defined in heap-symbols.h.

Bug: v8:8256
Cq-Include-Trybots: luci.v8.try:v8_linux_noi18n_rel_ng
Change-Id: I65dbc34639064d6d4c7d1786405b8b3af666bc2a
Reviewed-on: https://chromium-review.googlesource.com/c/1268761Reviewed-by: Sathya Gunasekaran <gsathya@chromium.org>
Commit-Queue: Frank Tang <ftang@chromium.org>
Cr-Commit-Position: refs/heads/master@{#56456}

src/objects/intl-objects.cc

@@ -1144,7 +1144,7 @@ Maybe<bool> Intl::SetNumberFormatDigitOptions(Isolate* isolate,
   // 9.  Let mnsd be ? Get(options, "minimumSignificantDigits").
   Handle<Object> mnsd_obj;
   Handle<String> mnsd_str =
-      isolate->factory()->NewStringFromStaticChars("minimumSignificantDigits");
+      isolate->factory()->minimumSignificantDigits_string();
   ASSIGN_RETURN_ON_EXCEPTION_VALUE(
       isolate, mnsd_obj, JSReceiver::GetProperty(isolate, options, mnsd_str),
       Nothing<bool>());
@@ -1152,7 +1152,7 @@ Maybe<bool> Intl::SetNumberFormatDigitOptions(Isolate* isolate,
   // 10. Let mxsd be ? Get(options, "maximumSignificantDigits").
   Handle<Object> mxsd_obj;
   Handle<String> mxsd_str =
-      isolate->factory()->NewStringFromStaticChars("maximumSignificantDigits");
+      isolate->factory()->maximumSignificantDigits_string();
   ASSIGN_RETURN_ON_EXCEPTION_VALUE(
       isolate, mxsd_obj, JSReceiver::GetProperty(isolate, options, mxsd_str),
       Nothing<bool>());