Simpler alternative to #103026 which avoids breaking compatibility.
Instead of introducing a new `auto` default value, we ensure that all
supported drivers are registered regardless of the editor's host platform,
and that the defaults are the intended ones.
This solves the following issues:
- macOS exports are meant to default to Metal in 4.4, but they would
default to Vulkan if exported from Linux, Windows, or Android editors.
- Windows exports couldn't be made with Direct3D 12 from Linux, macOS, or
Android editors, as the option couldn't be selected outside Windows.
Unlike #103026, it doesn't solve the issue of not always saving the
rendering drivers to `project.godot`, but now the defaults are at least
consistent between editor platforms.
Co-authored-by: Pāvels Nadtočajevs <7645683+bruvzg@users.noreply.github.com>
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