Initial implementation of GPUBuffer for WebGPU

Added WebIDL bindings for GPUBuffer, GPUBufferDescriptor, GPUBufferUsage
Implemented the `createBuffer` and `createBufferMapped` functions of GPUDevice

components/script/dom/gpubufferusage.rs

@@ -0,0 +1,11 @@
+/* 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/. */
+
+use crate::dom::bindings::reflector::Reflector;
+use dom_struct::dom_struct;
+
+#[dom_struct]
+pub struct GPUBufferUsage {
+    reflector_: Reflector,
+}