Make the templates of mocking api flexible

Rename mock_webgpu to mock_api and define the function "GetProcTableAndDevice" to "GetProcTable" for removing the special arguments "WGPUDevice* device" that can be got with "GetNewDevice()".

BUG=dawn:1201

Change-Id: I4fc47e4497ba4b6d280cc8af8605f1d93f43497e
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/72761
Reviewed-by: Jiawei Shao <jiawei.shao@intel.com>
Reviewed-by: Corentin Wallez <cwallez@chromium.org>
Reviewed-by: Austin Eng <enga@chromium.org>
Commit-Queue: Junwei Fu <junwei.fu@intel.com>

generator/templates/library_api_enum_tables.js

@@ -0,0 +1,35 @@
+//* Copyright 2020 The Dawn Authors
+//*
+//* Licensed under the Apache License, Version 2.0 (the "License");
+//* you may not use this file except in compliance with the License.
+//* You may obtain a copy of the License at
+//*
+//*     http://www.apache.org/licenses/LICENSE-2.0
+//*
+//* Unless required by applicable law or agreed to in writing, software
+//* distributed under the License is distributed on an "AS IS" BASIS,
+//* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+//* See the License for the specific language governing permissions and
+//* limitations under the License.
+//*
+//*
+//* This generator is used to produce the number-to-string mappings for
+//* Emscripten's library_webgpu.js.
+//* https://github.com/emscripten-core/emscripten/blob/master/src/library_webgpu.js
+//*
+    {% for type in by_category["enum"] if not type.json_data.get("emscripten_no_enum_table") %}
+        {{type.name.CamelCase()}}: {% if type.contiguousFromZero -%}
+            [
+                {% for value in type.values %}
+                  {{as_jsEnumValue(value)}},
+                {% endfor %}
+            ]
+        {%- else -%}
+            {
+                {% for value in type.values %}
+                  {{value.value}}: {{as_jsEnumValue(value)}},
+                {% endfor %}
+            }
+        {%- endif -%}
+        ,
+    {% endfor %}