Added (for compiler versions that support it):
-Wmissing-declarations
-Wzero-as-null-pointer-constant
Then, fixes to problems identified by the extra warnings
Tested only on GCC 9.4.0
Adjusted the CPP code generator to output nullptr where appropriate,
to satisfy -Wzero-as-null-pointer-constant
Added a lot of 'static' declarations in front of functions,
to satisfy -Wmissing-declarations,
and wrap static function defs in anonymous namespaces.
There are advantages to both anonymous namespaces and static,
it seems that marking a function as static will not publish the name in
the symbol table at all, thus giving the linker less work to do.
* 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
