Move canvas mode GL mappings to renderer gl

docs/modernization/build-inventory.md

@@ -202,6 +202,9 @@ Known local toolchain state:
   Desktop VR drawing also consumes backend-owned scissor/depth/blend state,
   depth clear masks, active texture units, and fallback 2D texture unbind
   targets while retaining the existing VR SDK/platform bridge shape.
+  Canvas mode overlay, mask, and transform paths also consume backend-owned
+  blend/depth state, active texture units, 2D texture copy targets, and RGBA8
+  readback format tokens.
 - `windows-msvc-vcpkg-headless` validates manifest install/configure/build/test
   for the current headless component matrix; see DEBT-0007 for remaining app
   and platform triplet migration.