[optimize/webpack] support __webpackPluginProvider__ uiExports (#17281) (#17285)

Allow plugins to integrate more deeply with webpack where necessary by supporting `__webpackPluginProvider__` uiExports which will be called and expected to return a wepack plugin that will be included in the compiler configuration that Kibana uses.

src/optimize/base_optimizer.js

@@ -153,6 +153,9 @@ export default class BaseOptimizer {
         }),
 
         new webpack.NoEmitOnErrorsPlugin(),
+
+        ...this.uiBundles.getWebpackPluginProviders()
+          .map(provider => provider(webpack)),
       ],
 
       module: {

src/ui/ui_bundles/ui_bundles_controller.js

@@ -48,6 +48,7 @@ export class UiBundlesController {
       ...getWebpackAliases(pluginSpecs),
       ...uiExports.webpackAliases
     };
+    this._webpackPluginProviders = uiExports.webpackPluginProviders;
     this._webpackNoParseRules = uiExports.webpackNoParseRules;
     this._postLoaders = [];
     this._bundles = [];
@@ -78,6 +79,10 @@ export class UiBundlesController {
     }
   }
 
+  getWebpackPluginProviders() {
+    return this._webpackPluginProviders || [];
+  }
+
   getWebpackNoParseRules() {
     return this._webpackNoParseRules;
   }

src/ui/ui_exports/ui_export_types/index.js

@@ -54,4 +54,5 @@ export {
   noParse,
   __globalImportAliases__,
   __bundleProvider__,
+  __webpackPluginProvider__,
 } from './webpack_customizations';

src/ui/ui_exports/ui_export_types/webpack_customizations.js

@@ -7,6 +7,7 @@ import { alias, wrap, uniqueKeys, mapSpec } from './modify_reduce';
 
 export const __globalImportAliases__ = wrap(alias('webpackAliases'), uniqueKeys('__globalImportAliases__'), mergeAtType);
 export const __bundleProvider__ = wrap(alias('uiBundleProviders'), flatConcatAtType);
+export const __webpackPluginProvider__ = wrap(alias('webpackPluginProviders'), flatConcatAtType);
 export const noParse = wrap(
   alias('webpackNoParseRules'),
   mapSpec(rule => {