SF: make FrameTimeline more robust for fence errors

- Emit a valid timestamp to Perfetto when fence signal time is invalid
- Mark pending fences as invalid if a newer fence has signaled

Test: SF unit tests
Bug: 243939707
Change-Id: Ieac7eb53fe3e36178d860cc0683bfd8fad7560cd
diff --git a/services/surfaceflinger/FrameTimeline/FrameTimeline.h b/services/surfaceflinger/FrameTimeline/FrameTimeline.h
index a2305af..31074b1 100644
--- a/services/surfaceflinger/FrameTimeline/FrameTimeline.h
+++ b/services/surfaceflinger/FrameTimeline/FrameTimeline.h
@@ -474,6 +474,7 @@
     friend class android::frametimeline::FrameTimelineTest;
 
     void flushPendingPresentFences() REQUIRES(mMutex);
+    std::optional<size_t> getFirstSignalFenceIndex() const REQUIRES(mMutex);
     void finalizeCurrentDisplayFrame() REQUIRES(mMutex);
     void dumpAll(std::string& result);
     void dumpJank(std::string& result);