Add ids to flatbuffer fields in y2012, y2016, frc971, and aos

Change-Id: I9ed9006ce6224e2df0459df47771786b928164a1
diff --git a/frc971/wpilib/loop_output_handler_test.fbs b/frc971/wpilib/loop_output_handler_test.fbs
index ddd36d0..7bcb91b 100644
--- a/frc971/wpilib/loop_output_handler_test.fbs
+++ b/frc971/wpilib/loop_output_handler_test.fbs
@@ -2,7 +2,7 @@
 
 // Test output message.
 table LoopOutputHandlerTestOutput {
-  voltage:double;
+  voltage:double (id: 0);
 }
 
 root_type LoopOutputHandlerTestOutput;