Creates an OPTIONS handler that handles any OPTIONS requests that are
not already handled by a handler. CORS has no mechanism to ensure the
user is authenticated, so the Router will reject cross-origin requests
from anon users.
This change allows authenticated users to make cross-origin
requests if they authenticate with OAuth or if
$wgRestAllowCrossOriginCookieAuth is enabled.
Bug: T232176
Bug: T262712
Change-Id: I128b4bdbec4f6bea35142153c951fd7b79617106
