Bump MoltenVK to 1.2.6 (Vulkan 1.3.268)

[shinra-electric]

New MoltenVK 1.2.6 release

New features or changes include:

• Add support for extensions:
  • VK_KHR_synchronization2
  • VK_EXT_extended_dynamic_state (requires Metal 3.1 for VK_DYNAMIC_STATE_VERTEX_INPUT_BINDING_STRIDE)
  • VK_EXT_extended_dynamic_state2
• Fix rare case where vertex attribute buffers are not bound to Metal when no other bindings change between pipelines.
• Ensure objects retained for life of MTLCommandBuffer during vkCmdBlitImage() & vkQueuePresentKHR().
• Fix case where a CAMetalDrawable with invalid pixel format causes onscreen flickering.
• Fix deadlock when reporting debug message on MVKInstance destruction.
• Fix MSL code used in vkCmdBlitImage() on depth-stencil formats.
• Improve behavior of swapchain image presentation stalls caused by Metal regression.
• VkPhysicalDeviceLimits::timestampPeriod set to 1.0 on Apple GPUs, and calculated dynamically on non-Apple GPUs.
• Add MVKConfiguration::timestampPeriodLowPassAlpha and environment variable MVK_CONFIG_TIMESTAMP_PERIOD_LOWPASS_ALPHA, to add a configurable lowpass filter for varying VkPhysicalDeviceLimits::timestampPeriod on non-Apple GPUs.
• Add several additional performance trackers, available via logging, or the mvk_private_api.h API.
• Deprecate MVK_DEBUG env var, and add MVK_CONFIG_DEBUG env var to replace it.
• Update MVK_CONFIGURATION_API_VERSION and MVK_PRIVATE_API_VERSION to 38.
• Update dependency libraries to match Vulkan SDK 1.3.268.
• Update to latest SPIRV-Cross:
  • MSL: Workaround Metal 3.1 regression bug on recursive input structs.
  • MSL: fix extraction of global variables, in case of atomics.
  • MSL: Workaround bizarre crash on macOS.
  • MSL: runtime array over argument buffers.
  • MSL: Make rw texture fences optional.
  • MSL: Prevent RAW hazards on read_write textures.