Initial implementation of GPUPipelineLayout for WebGPU

Added WebIDL bindings for `GPUPipelineLayout`.
Implemented the createPipelineLayout function of `GPUDevice`.

components/script/dom/gpubindgrouplayout.rs

@@ -42,6 +42,7 @@ impl GPUBindGroupLayout {
             valid: Cell::new(valid),
         }
     }
+
     pub fn new(
         global: &GlobalScope,
         channel: WebGPU,
@@ -62,6 +63,20 @@ impl GPUBindGroupLayout {
     }
 }
 
+impl GPUBindGroupLayout {
+    pub fn is_valid(&self) -> bool {
+        self.valid.get()
+    }
+
+    pub fn id(&self) -> WebGPUBindGroupLayout {
+        self.bind_group_layout
+    }
+
+    pub fn bindings(&self) -> &[GPUBindGroupLayoutBindings] {
+        &self.bindings
+    }
+}
+
 impl GPUBindGroupLayoutMethods for GPUBindGroupLayout {
     /// https://gpuweb.github.io/gpuweb/#dom-gpuobjectbase-label
     fn GetLabel(&self) -> Option<DOMString> {