[magma] Plumb context ID to magma decoder

This change makes the RenderThread's context ID visible to the magma
decoder. This will be needed for secure use of guest-allocated
buffers.

Bug: b/277219980
Test: m libgfxstream_backend
Change-Id: I482fee58b9513e252cf62f414366d299d111adf1
diff --git a/stream-servers/RenderThread.cpp b/stream-servers/RenderThread.cpp
index d014795..195ec6a 100644
--- a/stream-servers/RenderThread.cpp
+++ b/stream-servers/RenderThread.cpp
@@ -298,7 +298,7 @@
         tInfo.m_vkInfo.emplace();
     }
 
-    tInfo.m_magmaInfo.emplace();
+    tInfo.m_magmaInfo.emplace(mContextId);
 
     // This is the only place where we try loading from snapshot.
     // But the context bind / restoration will be delayed after receiving