Merge pull request #6472 from murgatroid99/ruby_signal_handling2

src/ruby/ext/grpc/rb_grpc.c

src/ruby/ext/grpc/rb_signal.c

src/ruby/ext/grpc/rb_signal.h

src/ruby/lib/grpc.rb

src/ruby/lib/grpc/generic/active_call.rb

src/ruby/lib/grpc/generic/rpc_server.rb

src/ruby/lib/grpc/signals.rb