Do not queue coalesced undecryptable packets twice

This CL adds QuicFramerVisitorInterface::OnUndecryptablePacket and uses it to send undecryptable packets from QuicFramer to QuicConnection, instead of the previous mechanism which relied on QuicFramer::ProcessPacket returning QUIC_DECRYPTION_FAILURE. The new mechanism has the following advantages:
1) It only sends the current packet, without any subsequent coalesced packets
2) It knows if the decryption failed due to a missing key, which allows us to avoid buffering packets that we know we will never be able to decrypt

This mechanism is enabled for versions that KnowsWhichDecrypterToUse() (which are v47+ || TLS, none of which are currently enabled) and when the new flag quic_framer_uses_undecryptable_upcall is true - the intent being to enable this for all versions once the flag protection process is complete.

This CL also adds QuicDataReader::FullPayload which is required to extract only this packet without further coalesced packets, and associated test.

gfe-relnote: do not queue coalesced undecryptable packets twice, protected by disabled flag gfe2_restart_flag_quic_framer_uses_undecryptable_upcall
PiperOrigin-RevId: 263658152
Change-Id: I66aca2138e353306a5cf4fa9ec259680f4115890
diff --git a/quic/test_tools/quic_test_utils.cc b/quic/test_tools/quic_test_utils.cc
index f03f06b..ed8c551 100644
--- a/quic/test_tools/quic_test_utils.cc
+++ b/quic/test_tools/quic_test_utils.cc
@@ -259,6 +259,11 @@
 void NoOpFramerVisitor::OnCoalescedPacket(
     const QuicEncryptedPacket& /*packet*/) {}
 
+void NoOpFramerVisitor::OnUndecryptablePacket(
+    const QuicEncryptedPacket& /*packet*/,
+    EncryptionLevel /*decryption_level*/,
+    bool /*has_decryption_key*/) {}
+
 bool NoOpFramerVisitor::OnStreamFrame(const QuicStreamFrame& /*frame*/) {
   return true;
 }