mod_proxy: Fix canonicalisation and FCGI env (PATH_INFO, SCRIPT_NAME) for

mod_proxy: Fix canonicalisation and FCGI env (PATH_INFO, SCRIPT_NAME) for
           "balancer:" URLs set via SetHandler, also allowing for "unix:"
           sockets with BalancerMember(s).  PR 69168.

* modules/proxy/proxy_util.h, modules/proxy/proxy_util.c:
  Move proxy_interpolate() from mod_proxy.c to ap_proxy_interpolate(),
  exported locally only (non public).
  Move proxy_fixup() from mod_proxy.c to ap_proxy_canon_url(), exported
  locally only too (non public).
  Rollback ap_proxy_fixup_uds_filename() to a local fixup_uds_filename()
  usable from proxy_util.c only. The public function will be removed in
  a following commit.

* modules/proxy/mod_proxy.h:
  Note that ap_proxy_fixup_uds_filename() is deprecated.

* modules/proxy/mod_proxy.c:
  Just use ap_proxy_canon_url() from proxy_fixup() and proxy_handler()
  for SetHandler URLs.

* modules/proxy/mod_proxy_balancer.c:
  Do not canonicalize the path from proxy_balancer_canon() anymore but
  rather from balancer_fixup() where the balancer URL is rewritten to
  the BalancerMember URL.

git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@1919022 13f79535-47bb-0310-9956-ffa450edef68