Initial implementation of GPUComputePipeline

Added WebIDL bindings for `GPUComputePipeline`.
Implemented the `createComputePipeline` function of `GPUDevice`.

components/script/dom/webidls/GPUComputePipeline.webidl

@@ -0,0 +1,22 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at https://mozilla.org/MPL/2.0/. */
+
+// https://gpuweb.github.io/gpuweb/#gpucomputepipeline
+[Exposed=(Window, DedicatedWorker), Serializable, Pref="dom.webgpu.enabled"]
+interface GPUComputePipeline {
+};
+GPUComputePipeline includes GPUObjectBase;
+
+dictionary GPUPipelineDescriptorBase : GPUObjectDescriptorBase {
+    required GPUPipelineLayout layout;
+};
+
+dictionary GPUProgrammableStageDescriptor {
+    required GPUShaderModule module;
+    required DOMString entryPoint;
+};
+
+dictionary GPUComputePipelineDescriptor : GPUPipelineDescriptorBase {
+    required GPUProgrammableStageDescriptor computeStage;
+};