Add spotless plugin and enforce header for java files (#2722)

This only applies to .java files changed compared to the origin base
branch (3.3.x):

 - Ensure tab indentation is used, with regexp fix for comment blocks
 - Trim trailing whitespaces
 - Ensure files end with a blank line
 - Remove unused imports
 - Enfore license header with up-to-date end year

build.gradle

@@ -39,6 +39,7 @@ plugins {
 	id 'biz.aQute.bnd.builder' version '5.0.1' apply false
 	id 'io.spring.nohttp' version '0.0.5.RELEASE'
 	id "io.github.reyerizo.gradle.jcstress" version "0.8.11" apply false
+	id "com.diffplug.spotless" version "5.14.0"
 }
 
 apply plugin: "io.reactor.gradle.detect-ci"
@@ -106,6 +107,20 @@ nohttp {
 	allowlistFile = project.file('codequality/nohttp/allowlist.lines')
 }
 
+spotless {
+	ratchetFrom 'origin/pivotalToVmware' //FIXME switch to 3.3.x once other PR is merged, and `main` once forward-merged
+	java {
+		target '**/*.java'
+		indentWithTabs()
+		replaceRegex 'class-level javadoc indentation fix', /^\*/, ' *'
+		replaceRegex 'method-level javadoc indentation fix', /\t\*/, '\t *'
+		trimTrailingWhitespace()
+		endWithNewline()
+		removeUnusedImports()
+		licenseHeaderFile('codequality/spotless/licenseJava.txt')
+	}
+}
+
 configure(subprojects) { p ->
 	apply plugin: 'java'
 	apply plugin: 'jacoco'

codequality/spotless/licenseJava.txt

@@ -0,0 +1,15 @@
+/*
+ * Copyright (c) 2011-$YEAR VMware Inc. or its affiliates, All Rights Reserved.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *   https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */