Merge r1836381, r1836382, r1836383, r1836386, r1836603 from trunk:

* 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


* Remove invalid copy and paste comments

* Always retrieve conditional function. static variable might contain garbage if module was reloaded in a static build.

* Add missing log numbers

* ap_proxy_balancer_get_best_worker cannot be exported and used as an optional
  function at the same time. So rename ap_proxy_balancer_get_best_worker to
  proxy_balancer_get_best_worker and make it static which is then used as an
  optional function and recreate ap_proxy_balancer_get_best_worker as an
  exported thin wrapper of proxy_balancer_get_best_worker.

Submitted by: rpluem
Reviewed by: covener, jim, ylavic


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/2.4.x@1840548 13f79535-47bb-0310-9956-ffa450edef68