grpc bindings generator for Java and a few minor supporting changes i… (#4553)

* grpc bindings generator for Java and a few minor supporting changes in improvements

* restored formatting before my previous changes for ease of review

* Fixed grpc java code generation bug resulting in duplicate extractor declarations in case the same is used in more than a single RPC method
diff --git a/CMakeLists.txt b/CMakeLists.txt
index 238ecdc..acae9fe 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -60,6 +60,8 @@
   grpc/src/compiler/cpp_generator.cc
   grpc/src/compiler/go_generator.h
   grpc/src/compiler/go_generator.cc
+  grpc/src/compiler/java_generator.h
+  grpc/src/compiler/java_generator.cc
 )
 
 set(FlatHash_SRCS