Metal: Distinguish Metal backend from OpenGL's Metal driver

On macOS 11+ OpenGL is implemented on top of Metal internally.
This CL changes ANGLE's Metal backend's renderer string to better
differentiate it from the above OpenGL renderer.

Bug: angleproject:5841
Change-Id: I0d5466594e385cb663d537db034c82b006b6e907
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2820179
Reviewed-by: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Jonah Ryan-Davis <jonahr@google.com>

src/libANGLE/renderer/metal/DisplayMtl.mm

@@ -139,7 +139,7 @@ std::string DisplayMtl::getRendererDescription()
 {
     ANGLE_MTL_OBJC_SCOPE
     {
-        std::string desc = "Metal Renderer";
+        std::string desc = "ANGLE Metal Renderer";
 
         if (mMetalDevice)
         {

src/tests/gl_tests/ImageTest.cpp

@@ -1005,10 +1005,6 @@ TEST_P(ImageTest, ANGLEExtensionAvailability)
     }
     else if (IsMetal())
     {
-        // http://anglebug.com/5814
-        // http://anglebug.com/5841 (wrong detection of IsMetal() on macOS 11)
-        ANGLE_SKIP_TEST_IF(IsARM64());
-
         // NOTE(hqle): Metal currently doesn't implement any image extensions besides
         // EGL_ANGLE_metal_texture_client_buffer
         EXPECT_TRUE(hasOESExt());

src/tests/test_utils/angle_test_platform.cpp

@@ -77,7 +77,7 @@ bool IsMetal()
 {
     const char *renderer = reinterpret_cast<const char *>(glGetString(GL_RENDERER));
     std::string rendererString(renderer);
-    return (rendererString.find("Metal") != std::string::npos);
+    return (rendererString.find("ANGLE Metal") != std::string::npos);
 }
 
 bool IsD3D()