Add trace slices to capture tasks important for latency monitoring

Add a trace slices for:
    - for all post composition work on main thread
    - transaction callbacks
    - screenshot work on main thread

Flag: EXEMPT adding trace slices + trivial refactor

Bug: 333623207
Test: perfetto
Change-Id: I6ca0a80941327edc0c78decf82176459d15d4595
diff --git a/services/surfaceflinger/SurfaceFlinger.h b/services/surfaceflinger/SurfaceFlinger.h
index ee541c4..34f48cd 100644
--- a/services/surfaceflinger/SurfaceFlinger.h
+++ b/services/surfaceflinger/SurfaceFlinger.h
@@ -896,7 +896,7 @@
 
     using OutputCompositionState = compositionengine::impl::OutputCompositionState;
 
-    std::optional<OutputCompositionState> getDisplayAndLayerSnapshotsFromMainThread(
+    std::optional<OutputCompositionState> getSnapshotsFromMainThread(
             RenderAreaBuilderVariant& renderAreaBuilder,
             GetLayerSnapshotsFunction getLayerSnapshotsFn, std::vector<sp<LayerFE>>& layerFEs);