Instead of adding conditionally everywhere, write the condition once
in v8_maybe_icu and include that. Essentially,

  if (v8_enable_i18n_support) {
    public_deps = [
      "//third_party/icu",
    ]
  }

becomes

  public_deps = [
    ":v8_maybe_icu",
  ]

Bug: v8:8834
Change-Id: I091b14c85f1495a967eaa2b272904fdf41e6e7eb
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1532337
Auto-Submit: Jakob Gruber <jgruber@chromium.org>
Reviewed-by: Michael Achenbach <machenbach@chromium.org>
Commit-Queue: Jakob Gruber <jgruber@chromium.org>
Cr-Commit-Position: refs/heads/master@{#60739}