compiler: add build option to enable deprecated generated code

partially resolving #1469

The added option for java_plugin `enable_deprecated` is `true` by default in `java_plugin.cpp`, so the generated code for `TestService.java` (`compiler/build.gradle` not setting this option) has all deprecated interfaces and static bindService method.

`./build.gradle` and `examples/build.gradle` set this option explicitly to `false`, so all the other generated classes do not have deprecated code.

Will set `enable_deprecated` to `false` by default in future PR when we are ready.
diff --git a/build.gradle b/build.gradle
index 5fb0cf3..a6fce8b 100644
--- a/build.gradle
+++ b/build.gradle
@@ -95,7 +95,11 @@
                   // it's possible the version of protoc has been changed.
                   task.inputs.file "${rootProject.projectDir}/build.gradle"
                   task.plugins {
-                    grpc {}
+                    grpc {
+                      // To generate deprecated interfaces and static bindService method,
+                      // turn the enable_deprecated option to true below:
+                      option 'enable_deprecated=false'
+                    }
                   }
                 }
               }