LibGfx+LibWeb: Support DirectX-based WebGL on Windows

[ayeteadoe]

I initially tried to build off of the recent Vulkan work for Linux WebGL by using the VK_KHR_EXTERNAL_MEMORY_WIN32_EXTENSION_NAME device extension and VK_EXTERNAL_MEMORY_HANDLE_TYPE_D3D11_TEXTURE_BIT_KHR handle type when creating the VkImage. That was all working; however, I was unable to create the acutal EGL surface (or image) with EGL_D3D_TEXTURE_2D_SHARE_HANDLE_ANGLE from the vulkan-created shared handle.

It seems to only work with getting the shared handle from a D3D11 texture (https://github.com/Microsoft/angle/wiki/Interop-with-other-DirectX-code). So I switched to Direct 3D on Windows for skia to get a painting surface compatible with the texture, and it seems to just work™

Demo

https://github.com/user-attachments/assets/ef8d101a-5f7d-4efe-b1b3-662781f48d13

[ayeteadoe]

Oops, I just realized when I switched to using the D3D backend context for navigables, I missed updating BackingStoreManager to handle Windows now, as USE_VULKAN in reallocate_backing_stores is no longer used. This means we were falling back to bitmap wrapped backing stores.

So one more rebase incoming that will change that check to #if defined(USE_VULKAN) || defined(AK_OS_WINDOWS) in the LibWeb: Use D3D12 SkiaBackendContext for Navigables on Windows commit.

I initially missed this because I was only testing https://webglsamples.org on this branch. But the performance slowdown with the bitmap wrapped backing stores was very noticable when I finally tested https://ladybird.org compared to current master.

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