[Fix, Test] (ShaderTranspiler, DirectGLES): fold or lower dynamically indexed fragment outputs before ESSL emission - GLSL ES requires constant integral indices, so the OIT coefficient shader linked nothing on ANGLE and every translucent draw was a silent no-op

MobileGL/MG_IntegrationTest/CMakeLists.txt

@@ -64,6 +64,7 @@ add_executable(MobileGLIntegrationTest
     Scenarios/SwizzleAccessRoutineScenario.cpp
     Scenarios/ProgramPipelineScenario.cpp
     Scenarios/Glsl420DeclarationScenario.cpp
+    Scenarios/FragmentOutputArrayIndexScenario.cpp
 )
 
 target_include_directories(MobileGLIntegrationTest PRIVATE