Cleanup: Move WebCore::weekFormatInLDML() from LocalizedStrings to Locale class.

BUG=298020
TEST=none; no behavior changes

Review URL: https://chromiumcodereview.appspot.com/24523002

git-svn-id: svn://svn.chromium.org/blink/trunk@158353 bbb929c8-8fbe-4397-9dbb-9b2b20218538