For compatibility reasons, `vulkan` is kept as the technical default for the
setting, but projects created in Godot 4.6 and later will set `d3d12` as the
driver automatically.
Users upgrading to 4.6 are recommended to adopt `d3d12` as a default if it
fits their needs.
Enable `d3d12=yes` by default in SCons so that custom Windows builds include
Direct3D 12 support.
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