[WebGPU] Implement GPUSampleMask support

https://bugs.webkit.org/show_bug.cgi?id=251444
radar://103304584

Reviewed by Tadeu Zagallo.

webgpu:api,operation,render_pipeline,sample_mask:* is all
green locally in MiniBrowser after this change but there
is some timeout running it through WKTR so I did not update
the expectations.

* Source/WebGPU/WebGPU/RenderPipeline.mm:
(WebGPU::Device::createRenderPipeline):

Canonical link: https://commits.webkit.org/270535@main

Source/WebGPU/WebGPU/RenderPipeline.mm

@@ -31,6 +31,11 @@
 #import "Device.h"
 #import "Pipeline.h"
 
+// FIXME: remove after radar://104903411 or after we place the mask into the last buffer
+@interface NSObject ()
+- (void)setSampleMask:(NSUInteger)mask;
+@end
+
 namespace WebGPU {
 
 static MTLBlendOperation blendOperation(WGPUBlendOperation operation)
@@ -647,6 +652,9 @@ static WGPUTextureViewDimension convertViewDimension(WGSL::TextureViewDimension
 
     mtlRenderPipelineDescriptor.rasterSampleCount = descriptor.multisample.count ?: 1;
     mtlRenderPipelineDescriptor.alphaToCoverageEnabled = descriptor.multisample.alphaToCoverageEnabled;
+    RELEASE_ASSERT([mtlRenderPipelineDescriptor respondsToSelector:@selector(setSampleMask:)]);
+    if (auto mask = descriptor.multisample.mask; mask != 0xFFFFFFFF)
+        [mtlRenderPipelineDescriptor setSampleMask:mask];
 
     if (descriptor.vertex.bufferCount)
         mtlRenderPipelineDescriptor.vertexDescriptor = createVertexDescriptor(descriptor.vertex);