Revert "Revert "Add ExternalTexture class into RenderEngine inte..."

Revert submission 14199598-revert-14086921-renderengine-external-tex-QJNBWQMQEU

Reason for revert: Prepare for relanding
Reverted Changes:
I01e65a7f4:Revert "Update WaylandRenderSurface to accomodate ...
I7d58118c1:Revert "Update Readback VTS to align with RenderEn...
I1501890f4:Revert "Add ExternalTexture class into RenderEngin...

Added the following fixes:
1. CachedSet renders to intermediate texture variable rather than
mTexture directly, since mTexture is not guaranteed to be nonnull.
2. Add null check when setting new buffer in BLAST.

Bug: 185524947
Bug: 180767535
Test: builds, boots
Test: librenderengine_test
Change-Id: I52ea82e24336b496d996bbe3e445db0affe1abb8
diff --git a/libs/renderengine/Android.bp b/libs/renderengine/Android.bp
index ec39137..f395ab4 100644
--- a/libs/renderengine/Android.bp
+++ b/libs/renderengine/Android.bp
@@ -48,6 +48,7 @@
     name: "librenderengine_sources",
     srcs: [
         "Description.cpp",
+        "ExternalTexture.cpp",
         "Mesh.cpp",
         "RenderEngine.cpp",
         "Texture.cpp",