Provide a function that converts grpc_call_error values into a string

grpc.def

include/grpc/grpc.h

src/core/lib/surface/call.c

src/python/grpcio/grpc/_cython/imports.generated.c

src/python/grpcio/grpc/_cython/imports.generated.h

src/ruby/ext/grpc/rb_grpc_imports.generated.c

src/ruby/ext/grpc/rb_grpc_imports.generated.h