Convert Velocity buildscripts to Kotlin DSL (#918)

Spiritually indebted to #518 and @alexstaeding.

There's a minor break - we're going up to 3.2.0-SNAPSHOT as the API now compiles against Java 11. But this is more academic in practice.

proxy/src/main/resources/log4j2.xml

@@ -32,7 +32,8 @@
     <RollingRandomAccessFile name="File" fileName="logs/latest.log"
       filePattern="logs/%d{yyyy-MM-dd}-%i.log.gz"
       immediateFlush="false">
-      <PatternLayout pattern="[%d{HH:mm:ss}] [%t/%level] [%logger]: %minecraftFormatting{%msg}{strip}%n"/>
+      <PatternLayout
+        pattern="[%d{HH:mm:ss}] [%t/%level] [%logger]: %minecraftFormatting{%msg}{strip}%n"/>
       <Policies>
         <TimeBasedTriggeringPolicy/>
         <OnStartupTriggeringPolicy/>