Backends: OpenGL3: Update loader to include APIs used by test framework.
Backends: OpenGL3: Update loader to include APIs used by test framework.

bkaradzic/imgui,ggtucker/imgui,nProtect/imgui,Flix01/imgui,nProtect/imgui,nProtect/imgui,bkaradzic/imgui,ggtucker/imgui,bkaradzic/imgui,Flix01/imgui,ggtucker/imgui,ocornut/imgui,ocornut/imgui,ocornut/imgui,Flix01/imgui