fuchsia: Use BGRA8 on non-ARM devices.

Change #23488
has switched all the Vulkan surfaces on Fuchsia to use
RGBA8 color type. However, Using RGBA8 format on Intel GPUs
has caused graphical artifacts on emulators
(See http://fxbug.dev/70232).

This change reverts the default vulkan format of Vulkan
surfaces to BGRA8 for non-ARM devices to fix the artifacts.

Bug: fxbug.dev/70232

Author: gnoliyil

shell/platform/fuchsia/flutter/vulkan_surface.cc

@@ -26,9 +26,21 @@ namespace flutter_runner {
 
 namespace {
 
+// Immutable format is technically limited to R8G8B8A8_SRGB but
+// R8G8B8A8_UNORM works with existing ARM drivers so we allow that
+// until we have a more reliable API for creating external Vulkan
+// images using sysmem. TODO(fxb/52835)
+#if defined(__aarch64__)
 constexpr SkColorType kSkiaColorType = kRGBA_8888_SkColorType;
 constexpr VkFormat kVulkanFormat = VK_FORMAT_R8G8B8A8_UNORM;
 constexpr VkImageCreateFlags kVulkanImageCreateFlags = 0;
+#else
+constexpr SkColorType kSkiaColorType = kBGRA_8888_SkColorType;
+constexpr VkFormat kVulkanFormat = VK_FORMAT_B8G8R8A8_UNORM;
+constexpr VkImageCreateFlags kVulkanImageCreateFlags =
+    VK_IMAGE_CREATE_MUTABLE_FORMAT_BIT;
+#endif
+
 // TODO: We should only keep usages that are actually required by Skia.
 constexpr VkImageUsageFlags kVkImageUsage =
     VK_IMAGE_USAGE_COLOR_ATTACHMENT_BIT | VK_IMAGE_USAGE_TRANSFER_DST_BIT |