Add Metal swapchain presentation options

[tryk016]

Adds per-swapchain options for two or three drawables and direct rendering into the drawable texture.

Defaults stay unchanged. Direct rendering avoids the private color buffers and the final copy, with a copy fallback when a matching drawable is unavailable. Recorded frames are kept alive until the GPU has finished using them.

Tested on macOS, iOS 18/27 simulators and an iPhone 15 Pro Max, including pixel readback, reset, fallback and resource lifetime checks.

Also tested in OpenGothic on macOS with Copy/Direct and both buffer counts.

[Try]

Hi, @tryk016 !

Private color buffers are there because engine initially was build with Vulkan-like abstraction (and eventually DX12-like) over swapchain.
On DX12/Vulkan images are persistent, and application can LOAD_OP_LOAD them in next frames, or keep references to image-data and expect those to be valid until reset.

However this abstraction no longer relevant, and rather then patch current swapchain we should move to implementation that makes more sense.
In #110 I only drafted idea outline. Basically swapchain image can have very short life-time on game-side (single-frame only), like it is in Metal.