ESQL: Disable format checks on generated imports (elastic#127648)

This builds the infrastructure to disable spotless and some checkstyle
rules on generated imports. This works around the most frustrating part
of ESQL's string template generated files - the imports. It allows
unused and out of order imports. This can let us remove a lot of
cumbersome, tricky, and fairly useless `$if$` blocks from the templates.

Author: nik9000

build-tools-internal/src/main/resources/checkstyle.xml

@@ -68,6 +68,11 @@
 
     <!-- Unused imports are forbidden -->
     <module name="UnusedImports" />
+    <module name="SuppressionCommentFilter">
+      <property name="offCommentFormat" value="begin generated imports"/>
+      <property name="onCommentFormat" value="end generated imports"/>
+      <property name="checkFormat" value="UnusedImports"/>
+    </module>
 
     <!-- Non-inner classes must be in files that match their names. -->
     <module name="OuterTypeFilename" />

x-pack/plugin/esql/compute/build.gradle

@@ -49,6 +49,7 @@ spotless {
     /*
      * Generated files go here.
      */
+    toggleOffOn('begin generated imports', 'end generated imports')
     targetExclude "src/main/generated/**/*.java"
   }
 }

x-pack/plugin/esql/compute/src/main/generated-src/org/elasticsearch/compute/data/BooleanArrayVector.java

@@ -7,7 +7,7 @@
 
 package org.elasticsearch.compute.data;
 
-$if(BytesRef)$
+// begin generated imports
 import org.apache.lucene.util.BytesRef;
 import org.apache.lucene.util.RamUsageEstimator;
 import org.elasticsearch.common.io.stream.StreamInput;
@@ -17,19 +17,10 @@ import org.elasticsearch.common.util.BytesRefArray;
 import org.elasticsearch.core.ReleasableIterator;
 import org.elasticsearch.core.Releasables;
 
-import java.io.IOException;
-
-$else$
-import org.apache.lucene.util.RamUsageEstimator;
-import org.elasticsearch.common.io.stream.StreamInput;
-import org.elasticsearch.common.io.stream.StreamOutput;
-import org.elasticsearch.common.unit.ByteSizeValue;
-import org.elasticsearch.core.ReleasableIterator;
-
 import java.io.IOException;
 import java.util.stream.Collectors;
 import java.util.stream.IntStream;
-$endif$
+// end generated imports
 
 /**
  * Vector implementation that stores an array of $type$ values.