Performance/Webpack: Introduces more aggressive code-splitting and other perf improvements (#18544)

* Performance/Webpack: Introduces more aggressive code-splitting and other perf improvements
- Introduces dynamic imports for built-in plugins
- Uses dynamic imports for various packages (rst2html, brace)
- Introduces route-based dynamic imports
- Splits angular and moment into separate bundles

public/app/plugins/datasource/stackdriver/components/Alignments.tsx

@@ -1,5 +1,4 @@
 import React, { FC } from 'react';
-import _ from 'lodash';
 
 import { MetricSelect } from 'app/core/components/Select/MetricSelect';
 import { TemplateSrv } from 'app/features/templating/template_srv';

public/app/plugins/datasource/stackdriver/query_ctrl.ts

@@ -1,5 +1,3 @@
-import _ from 'lodash';
-
 import { QueryCtrl } from 'app/plugins/sdk';
 import { StackdriverQuery } from './types';
 import { TemplateSrv } from 'app/features/templating/template_srv';