[Metal] Descriptor set layout bindings out-of-bounds access and unsorted bindings invariant violation

Describe the bug There are two related descriptor set handling issues in the Metal backend when handling sparse/high binding indices and unsorted bindings:

1. Out-of-bounds indexing in MetalDriver::updateDescriptorSetBuffer: In filament/backend/src/metal/MetalDriver.mm:

   cpp复制

   ShaderStageFlags stageFlags = descriptorSet->layout->getBindings()[binding].stageFlags;

   descriptorSet->layout->getBindings() returns mLayout.descriptors, which is an array with size equal to the descriptor count (e.g. 3 bindings). Indexing directly by [binding] assumes contiguous 0-based binding indices matching array indices. When a descriptor set has sparse or high binding indices (e.g. binding 32 or 63), getBindings()[binding] accesses out of bounds, causing memory corruption or crash. In contrast, MetalDriver::updateDescriptorSetTexture correctly looks up the binding via std::find_if:

   cpp复制

   auto const& bindings = descriptorSet->layout->getBindings();
   auto found = std::find_if(bindings.begin(), bindings.end(),
           [binding](const auto& b) { return b.binding == binding; });

2. Binding sort invariant trapped inside #if FILAMENT_METAL_DEBUG_LOG == 1: In filament/backend/src/metal/MetalHandles.mm:

   cpp复制

   // Important! The bindings must be sorted by binding number. This has already been done inside
   // createDescriptorSetLayout.

   However, in filament/backend/src/metal/MetalDriver.mm:

   cpp复制

   void MetalDriver::createDescriptorSetLayoutR(...) {
   #if FILAMENT_METAL_DEBUG_LOG == 1
       ...
       std::sort(info.descriptors.begin(), info.descriptors.end(),
               [](const auto& a, const auto& b) { return a.binding < b.binding; });
       ...
   #endif
       construct_handle<MetalDescriptorSetLayout>(dslh, std::move(info));
   }

   std::sort was accidentally placed inside the FILAMENT_METAL_DEBUG_LOG == 1 block. In standard release and debug builds, FILAMENT_METAL_DEBUG_LOG is 0, so bindings are never sorted. This violates the assumption in MetalDescriptorSetLayout::getArgumentEncoderSlow and can cause mismatched texture type indexing and broken argument encoder cache keys.

To Reproduce Steps to reproduce the behavior:

1. Create a DescriptorSetLayout with sparse/high binding indices, e.g. binding 0 and binding 32.
2. Create a descriptor set from the layout.
3. Call updateDescriptorSetBuffer on binding 32.
4. Observe out-of-bounds vector access in updateDescriptorSetBuffer.

Expected behavior

• updateDescriptorSetBuffer should locate the binding descriptor via lookup (std::find_if) rather than directly indexing getBindings()[binding].
• MetalDescriptorSetLayout or createDescriptorSetLayoutR should unconditionally sort descriptors by binding number regardless of debug logging macros.

Desktop (please complete the following information):

• OS: macOS / iOS
• Backend: Metal

Additional context Discovered while auditing descriptor set binding index limits and writing cross-backend tests.