Suppress checkstyle on generated files in painless

Closes #16387

buildSrc/src/main/groovy/org/elasticsearch/gradle/precommit/PrecommitTasks.groovy

@@ -94,6 +94,9 @@ class PrecommitTasks {
         project.checkstyle {
             config = project.resources.text.fromFile(
                 PrecommitTasks.getResource('/checkstyle.xml'), 'UTF-8')
+            configProperties = [
+                suppressions: PrecommitTasks.getResource('/checkstyle_suppressions.xml')
+            ]
         }
         for (String taskName : ['checkstyleMain', 'checkstyleTest']) {
             Task task = project.tasks.findByName(taskName)

buildSrc/src/main/resources/checkstyle.xml

@@ -6,6 +6,10 @@
 <module name="Checker">
   <property name="charset" value="UTF-8" />
 
+  <module name="SuppressionFilter">
+    <property name="file" value="${suppressions}" />
+  </module>
+
   <module name="TreeWalker">
     <!-- ~3500 violations
     <module name="LineLength">

buildSrc/src/main/resources/checkstyle_suppressions.xml

@@ -0,0 +1,10 @@
+<?xml version="1.0"?>
+<!DOCTYPE suppressions PUBLIC
+          "-//Puppy Crawl//DTD Suppressions 1.1//EN"
+          "http://www.puppycrawl.com/dtds/suppressions_1_1.dtd">
+
+<suppressions>
+  <!-- These files are generated by ANTLR so its silly to hold them to our rules. -->
+  <suppress files="org/elasticsearch/painless/PainlessLexer\.java" checks="." />
+  <suppress files="org/elasticsearch/painless/PainlessParser(|BaseVisitor|Visitor)\.java" checks="." />
+</suppressions>