Store previous buffer as a wp

Bug: 404177558
Flag: EXEMPT bug fix
Test: builds, boots
Change-Id: I21c27e69e70b1ec9b447d25f257d2fc57b1590c1

Author: AMouri

services/surfaceflinger/Layer.h

@@ -117,7 +117,7 @@ class Layer : public virtual RefBase {
         uint32_t bufferTransform;
         bool transformToDisplayInverse;
         Region transparentRegionHint;
-        std::shared_ptr<renderengine::ExternalTexture> previousBuffer;
+        std::weak_ptr<renderengine::ExternalTexture> previousBuffer;
         std::shared_ptr<renderengine::ExternalTexture> buffer;
         sp<Fence> acquireFence;
         std::shared_ptr<FenceTime> acquireFenceTime;