* mod_proxy: Remove load order and link dependency between mod_lbmethod_*

  modules and mod_proxy by providing mod_proxy's ap_proxy_balancer_get_best_worker
  as an optional function.

PR: 62557


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@1836381 13f79535-47bb-0310-9956-ffa450edef68