TraceProcessor RPC: Allow Serialize into protozero

The current QueryResultSerializer returns a
vector<uint8_t>. This doesn't work anymore with the
upcoming changes to the RPC which add a new layer
above (the root TraceProcessorRpc).
Instead switch the impl to take a protozero message
as argument, so the serializer can be chained.

Bug: 159142289
Test: perfetto_unittests --gtest_filter=QueryResultSerializerTest.*
Change-Id: I9f4c2738e1147f1198a74e509862e3a0b2d118ba

test/end_to_end_shared_memory_fuzzer.cc

diff --git a/test/end_to_end_shared_memory_fuzzer.cc b/test/end_to_end_shared_memory_fuzzer.cc
index ce53acf..782cc30 100644
--- a/test/end_to_end_shared_memory_fuzzer.cc
+++ b/test/end_to_end_shared_memory_fuzzer.cc
@@ -83,7 +83,7 @@
         static_cast<BufferID>(source_config.target_buffer()));
     {
       auto packet = trace_writer->NewTracePacket();
-      packet->stream_writer_for_testing()->WriteBytes(data_, size_);
+      packet->AppendRawProtoBytes(data_, size_);
     }
     trace_writer->Flush();