fix: properly set viewports and render targets for Apple Vision Pro

[okwasniewski]

This PR partially fixes issues with bgfx rendering on Apple Vision Pro devices. It aims to fix issues described in this Tweet: https://x.com/o_kwasniewski/status/1811313113527992391

Here is the outline of what this PR is doing:

• Correctly calculate and set the viewports for each eye
• Retrieve configuration layer_renderer
• Set Vertex Amplification to make both eyes see the content. (MRT - multiple render targets)
• Fixes issues with frame rendering function calls (now it's following Apple docs)
• Properly sets fields on renderPassDescriptor
• Warns users that BFGX does not support .dedicated layout at this point

[bkaradzic]

Also number of eyes is not arbitrary, so you don't have to use dynamic array type of containers for viewports at all... Consider what's maximum number of eyes you will ever have on VisionOS, and then create something more appropriate.

[okwasniewski]

Hey @bkaradzic thanks for reviewing, I removed STL references and allocated a static C-like array for the viewports.

[okwasniewski]

Hey @bkaradzic, anything you would like to see changed in this PR?

Just so you know, we are moving forward with the integration (currently by cherry-picking the changes) and we have made some progress. I'm attaching a video of Babylon Native running on the device, we still need to figure out 6DOF but it's on the Babylon side.

ScreenRecording.July.19.2024.mov