Instead of auto-generating the Name() convenience accessor, use a macro to
avoid wasting code space.

  BUILTIN_CODE(isolate, Name)

expands to

  isolate->builtins()->builtin_handle(Builtins::kName);

This reduces the size of libv8.so by 134,752 bytes on a x64 release build.

Bug: v8:6624
Cq-Include-Trybots: master.tryserver.chromium.linux:linux_chromium_rel_ng
Change-Id: Idff7ee5c45e344e73412c0f47e92553c7c7ff75f
Reviewed-on: https://chromium-review.googlesource.com/593607Reviewed-by: Andreas Haas <ahaas@chromium.org>
Reviewed-by: Benedikt Meurer <bmeurer@chromium.org>
Commit-Queue: Jakob Gruber <jgruber@chromium.org>
Cr-Commit-Position: refs/heads/master@{#47010}