Switch over to Error Prone (now with NullAway!)

There is one major change: we now have a separate artifact for the annotation processor.

As for NullAway, we are currently exempting the clientbound join game/respawn packets. They are ugly and need to be refactored.

build.gradle

@@ -9,12 +9,12 @@ buildscript {
 
 plugins {
     id 'java'
-    id "com.github.spotbugs" version "4.2.4" apply false
+    id "net.ltgt.errorprone" version "2.0.1" apply false
     id 'org.cadixdev.licenser' version '0.5.1' apply false
 }
 
 allprojects {
-    apply plugin: "com.github.spotbugs"
+    apply plugin: "net.ltgt.errorprone"
 
     group 'com.velocitypowered'
     version '2.0.0-SNAPSHOT'
@@ -67,14 +67,4 @@ allprojects {
             junitXml.enabled = true
         }
     }
-
-    tasks.withType(com.github.spotbugs.snom.SpotBugsTask) {
-        reports {
-            html {
-                enabled = true
-                destination = file("$buildDir/reports/spotbugs/main/spotbugs.html")
-                stylesheet = 'fancy-hist.xsl'
-            }
-        }
-    }
 }