Use IPSet for checking of wgProxyList

Use IPSet for checking of wgProxyList

Instead of using array_* functions, use the IPSet for checking, if a
specific IP address matches a set of addresses.

This also deprecates a backward-compatibility functionality, that
the wgProxyList array could also be an associative array, where the blocked
IP address is set as a key of the array insted of a value. All IP address
keys will be mved to values on-the-fly, however a deprecation warning will
be emitted. A notice in the Release notes was added, too.

Bug: T161580
Change-Id: I69d9534942c415ab044177969ecd54160079b593