[Fix] (DirectVulkan): raw sRGB attachment writes while FRAMEBUFFER_SRGB is off

GL renders into sRGB color attachments RAW when GL_FRAMEBUFFER_SRGB is
disabled (the core-profile default), but Vulkan sRGB attachments always
encode on write - one decode went missing whenever a rendered-into sRGB
texture was sampled again (multisampled sRGB targets in
texture_size_promotion and texture_swizzle idx27/28 ms cases).

Attachment views (textures and renderbuffers) now reinterpret sRGB
images through their UNORM twin while the capability is off, switching
back when enabled: images get MUTABLE_FORMAT, the attachment-view cache
keys the view format, renderbuffers carry a second view, and the render
pass hash includes the capability state. Sampled views keep decoding.
The VkTextureManager.cpp half of this rides with the next commit.

MobileGL/MG_Backend/DirectVulkan/Renderer/VkTextureManager.h

@@ -67,12 +67,16 @@ public:
             Uint32 baseArrayLayer = 0;
             Uint32 layerCount = 1;
             VkImageViewType viewType = VK_IMAGE_VIEW_TYPE_2D;
+            // May differ from the image format: sRGB images attach through their UNORM
+            // twin while GL_FRAMEBUFFER_SRGB is disabled.
+            VkFormat viewFormat = VK_FORMAT_UNDEFINED;
 
             Bool operator==(const AttachmentViewKey& other) const {
                 return mipLevel == other.mipLevel &&
                        baseArrayLayer == other.baseArrayLayer &&
                        layerCount == other.layerCount &&
-                       viewType == other.viewType;
+                       viewType == other.viewType &&
+                       viewFormat == other.viewFormat;
             }
         };
 
@@ -83,6 +87,8 @@ public:
                 hash ^= std::hash<Uint32>{}(key.layerCount) + 0x9e3779b9u + (hash << 6) + (hash >> 2);
                 hash ^= std::hash<Uint32>{}(static_cast<Uint32>(key.viewType)) +
                         0x9e3779b9u + (hash << 6) + (hash >> 2);
+                hash ^= std::hash<Uint32>{}(static_cast<Uint32>(key.viewFormat)) +
+                        0x9e3779b9u + (hash << 6) + (hash >> 2);
                 return hash;
             }
         };