MINOR: Optimise performance of `Topic.validate()`

I included a JMH benchmark and the results follow. The
implementation in this PR takes no more than 1/10th
of the time when compared to trunk. I also included
results for an alternative implementation that is a little
slower than the one in the PR.

Trunk:
```text
TopicBenchmark.testValidate                                topic  avgt   15  134.107 ±  3.956  ns/op
TopicBenchmark.testValidate                    longer-topic-name  avgt   15  316.241 ± 13.379  ns/op
TopicBenchmark.testValidate  very-long-topic-name_with_more_text  avgt   15  636.026 ± 30.272  ns/op
```

Implementation in the PR:
```text
TopicBenchmark.testValidate                                topic  avgt   15  13.153 ± 0.383  ns/op
TopicBenchmark.testValidate                    longer-topic-name  avgt   15  26.139 ± 0.896  ns/op
TopicBenchmark.testValidate  very-long-topic-name.with_more_text  avgt   15  44.829 ± 1.390  ns/op
```

Alternative implementation where boolean validChar = Character.isLetterOrDigit(c) || c == '.' || c == '_' || c == '-';
```text
TopicBenchmark.testValidate                                topic  avgt   15  18.883 ± 1.044  ns/op
TopicBenchmark.testValidate                    longer-topic-name  avgt   15  36.696 ± 1.220  ns/op
TopicBenchmark.testValidate  very-long-topic-name_with_more_text  avgt   15  65.956 ± 0.669  ns/op
```

Author: Ismael Juma <ismael@juma.me.uk>

Reviewers: Guozhang Wang <wangguoz@gmail.com>

Closes #3234 from ijuma/optimise-topic-is-valid

checkstyle/suppressions.xml

@@ -40,7 +40,7 @@
               files=".*/protocol/Errors.java"/>
 
     <suppress checks="BooleanExpressionComplexity"
-              files="(Utils|KafkaLZ4BlockOutputStream|AclData).java"/>
+              files="(Utils|Topic|KafkaLZ4BlockOutputStream|AclData).java"/>
 
     <suppress checks="CyclomaticComplexity"
               files="(ConsumerCoordinator|Fetcher|Sender|KafkaProducer|BufferPool|ConfigDef|RecordAccumulator|SsLTransportLayer|KerberosLogin|AbstractRequest|AbstractResponse|Selector|SslTransportLayer).java"/>

clients/src/main/java/org/apache/kafka/common/internals/Topic.java

@@ -21,7 +21,6 @@ import org.apache.kafka.common.utils.Utils;
 
 import java.util.Collections;
 import java.util.Set;
-import java.util.regex.Pattern;
 
 public class Topic {
 
@@ -33,7 +32,6 @@ public class Topic {
             Utils.mkSet(GROUP_METADATA_TOPIC_NAME, TRANSACTION_STATE_TOPIC_NAME));
 
     private static final int MAX_NAME_LENGTH = 249;
-    private static final Pattern LEGAL_CHARS_PATTERN = Pattern.compile(LEGAL_CHARS + "+");
 
     public static void validate(String topic) {
         if (topic.isEmpty())
@@ -77,6 +75,15 @@ public class Topic {
      * Valid characters for Kafka topics are the ASCII alphanumerics, '.', '_', and '-'
      */
     static boolean containsValidPattern(String topic) {
-        return LEGAL_CHARS_PATTERN.matcher(topic).matches();
+        for (int i = 0; i < topic.length(); ++i) {
+            char c = topic.charAt(i);
+
+            // We don't use Character.isLetterOrDigit(c) because it's slower
+            boolean validChar = (c >= 'a' && c <= 'z') || (c >= '0' && c <= '9') || (c >= 'A' && c <= 'Z') || c == '.' ||
+                    c == '_' || c == '-';
+            if (!validChar)
+                return false;
+        }
+        return true;
     }
 }

gradle/findbugs-exclude.xml

@@ -164,6 +164,7 @@ For a detailed description of findbugs bug categories, see http://findbugs.sourc
              benchmarking. -->
         <Or>
             <Package name="org.apache.kafka.jmh.cache.generated"/>
+            <Package name="org.apache.kafka.jmh.common.generated"/>
             <Package name="org.apache.kafka.jmh.record.generated"/>
             <Package name="org.apache.kafka.jmh.producer.generated"/>
         </Or>

jmh-benchmarks/src/main/java/org/apache/kafka/jmh/common/TopicBenchmark.java

@@ -0,0 +1,53 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements. See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You 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
+ *
+ *    http://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.
+ */
+package org.apache.kafka.jmh.common;
+
+import org.apache.kafka.common.internals.Topic;
+import org.openjdk.jmh.annotations.Benchmark;
+import org.openjdk.jmh.annotations.BenchmarkMode;
+import org.openjdk.jmh.annotations.Fork;
+import org.openjdk.jmh.annotations.Measurement;
+import org.openjdk.jmh.annotations.Mode;
+import org.openjdk.jmh.annotations.OutputTimeUnit;
+import org.openjdk.jmh.annotations.Param;
+import org.openjdk.jmh.annotations.Scope;
+import org.openjdk.jmh.annotations.State;
+import org.openjdk.jmh.annotations.Warmup;
+
+import java.util.concurrent.TimeUnit;
+
+@State(Scope.Benchmark)
+@Fork(value = 1)
+@Warmup(iterations = 5)
+@Measurement(iterations = 15)
+@BenchmarkMode(Mode.AverageTime)
+@OutputTimeUnit(TimeUnit.NANOSECONDS)
+public class TopicBenchmark {
+
+    @State(Scope.Thread)
+    public static class BenchState {
+        @Param({"topic", "longer-topic-name", "very-long-topic-name.with_more_text"})
+        public String topicName;
+    }
+
+    @Benchmark
+    public BenchState testValidate(BenchState state) {
+        // validate doesn't return anything, so return `state` to prevent the JVM from optimising the whole call away
+        Topic.validate(state.topicName);
+        return state;
+    }
+}