feat: add visionOS support

[okwasniewski]

Hello,

This PR adds visionOS support to bgfx. It's the continuation of this PR which added support to bx library. I've worked on this together with @mani3xis.

Apple Vision uses bgfx in single threaded mode (BGFX_CONFIG_MULTITHREADED = 0), but the example framework isn't really working nice with single threaded mode, so there might be some crashes in the examples but it works great when integrated separately.

[bkaradzic]

Follow existing file name convention when adding new files...

[bkaradzic]

Please split this into two PRs. One where you just add BX_PLATFORM_VISIONOS defines, and after that PR one where you add new files, change scripts, etc.

[bkaradzic]

You should investigate how to avoid using 4 files for visionOS entry. Ideally only one file would be there.

[okwasniewski]

Hey @bkaradzic,

I've removed "example" needed changes from this PR. I will open a separate one.

[okwasniewski]

Hey @bkaradzic, is there anything more I should change in this PR?

[okwasniewski]

Hey @bkaradzic! I did an initial testing integration to BabylonNative and it seems to work properly 👍🏻 Is there anything else you want to see in this PR fixed?

Here is a screenshot of Babylon Native examples running on visionOS (it's rendering a cube):

[bkaradzic]

LGTM! Only question about this code:

#if BX_PLATFORM_VISIONOS
        cp_layer_renderer_t m_layerRenderer;
        cp_frame_t m_frame;
        cp_drawable_t m_drawable;
#else
		CAMetalLayer* m_metalLayer;
		CAMetalLayer* m_metalLayer;
		id <CAMetalDrawable> m_drawable;
        id <CAMetalDrawable> m_drawable;
#endif

Is this cp_layer_renderer something new that's also available on other Apple platforms or it's specific to visionOS?!

[okwasniewski]

LGTM! Only question about this code:

#if BX_PLATFORM_VISIONOS
        cp_layer_renderer_t m_layerRenderer;
        cp_frame_t m_frame;
        cp_drawable_t m_drawable;
#else
		CAMetalLayer* m_metalLayer;
		CAMetalLayer* m_metalLayer;
		id <CAMetalDrawable> m_drawable;
        id <CAMetalDrawable> m_drawable;
#endif

Is this cp_layer_renderer something new that's also available on other Apple platforms or it's specific to visionOS?!

It's specific to visionOS, it's unavailable on other platforms.