Remove some concurrency and performance bottlenecks in SpecificRecord…

…Generator (#531)

* Make java file write wait by using reduce instead of count

* Remove unused pool

* Cleanup unused imports

* Make some shared global objects thread safe for concurrent access/modification

* Remove some concurrency and performance bottlenecks in SpecificRecordGenerator

---------

Co-authored-by: Karthik Ramgopal <kramgopa@linkedin.com>

avro-builder/builder/src/main/java/com/linkedin/avroutil1/builder/operations/codegen/own/AvroUtilCodeGenOp.java

@@ -250,9 +250,9 @@ public void run(OperationContext opContext) throws Exception {
       throw new IllegalStateException("unable to create output folder " + outputFolder);
     }
     final Path outputDirectoryPath = outputFolder.toPath();
+    final SpecificRecordClassGenerator generator = new SpecificRecordClassGenerator();
 
     int totalGeneratedClasses = allNamedSchemaList.parallelStream().map(allNamedSchemas -> {
-      SpecificRecordClassGenerator generator = new SpecificRecordClassGenerator();
       HashSet<String> alreadyGeneratedSchemaNames = new HashSet<>();
       List<JavaFile> generatedSpecificClasses = new ArrayList<>(allNamedSchemas.size());
       for (AvroNamedSchema namedSchema : allNamedSchemas) {