[composer] Add createCommandWriter to command engine.

Command engine always uses V2.1 CommandWriterBase, change the creation of
command writer inside command engine so that we can use the right version of
command writer.

This patch updates VR composer to match the change.

BUG: b/147365206
Test: build and boot.
Change-Id: I373768a80947a3856b10de72aac4ca72926fbee5
diff --git a/services/vr/hardware_composer/impl/vr_composer_client.cpp b/services/vr/hardware_composer/impl/vr_composer_client.cpp
index 36f6b32..dd1603d 100644
--- a/services/vr/hardware_composer/impl/vr_composer_client.cpp
+++ b/services/vr/hardware_composer/impl/vr_composer_client.cpp
@@ -73,7 +73,7 @@
 
   auto err = mVrHal.setLayerInfo(mCurrentDisplay, mCurrentLayer, read(), read());
   if (err != Error::NONE) {
-    mWriter.setError(getCommandLoc(), err);
+    mWriter->setError(getCommandLoc(), err);
   }
 
   return true;
@@ -86,7 +86,7 @@
 
   auto err = mVrHal.setClientTargetMetadata(mCurrentDisplay, readBufferMetadata());
   if (err != Error::NONE)
-    mWriter.setError(getCommandLoc(), err);
+    mWriter->setError(getCommandLoc(), err);
 
   return true;
 }
@@ -99,7 +99,7 @@
   auto err = mVrHal.setLayerBufferMetadata(mCurrentDisplay, mCurrentLayer,
                                            readBufferMetadata());
   if (err != Error::NONE)
-    mWriter.setError(getCommandLoc(), err);
+    mWriter->setError(getCommandLoc(), err);
 
   return true;
 }