blast: update hasDrawingBuffer to hasFrameUpdate

hasFrameUpdate is a more accurate name than hasDrawingBuffer.
Also keep track of when the current state has been modified
and only return true for BufferStateLayer::hasFrameUpdate
when the state has been modified and the buffer is not null.

Test: Transaction_test
Bug: 80477568

Change-Id: Icec6cf62490799988bd967914986bf92a07ce726
diff --git a/services/surfaceflinger/BufferLayer.h b/services/surfaceflinger/BufferLayer.h
index d000d85..187b34f 100644
--- a/services/surfaceflinger/BufferLayer.h
+++ b/services/surfaceflinger/BufferLayer.h
@@ -134,7 +134,7 @@
 
     virtual std::optional<Region> latchSidebandStream(bool& recomputeVisibleRegions) = 0;
 
-    virtual bool hasDrawingBuffer() const = 0;
+    virtual bool hasFrameUpdate() const = 0;
 
     virtual void setFilteringEnabled(bool enabled) = 0;