build(aio): add metadata aliases for directives, components and pipes (#19317)

This change will enable people to link to the API docs via their selectors
or names, as used in a template.

Since the selectors can be quite complex we are not able to get 100%
accuracy.

Closes #16787

aio/tools/transforms/angular-api-package/index.js

@@ -20,6 +20,7 @@ module.exports = new Package('angular-api', [basePackage, typeScriptPackage])
   .processor(require('./processors/mergeDecoratorDocs'))
   .processor(require('./processors/extractDecoratedClasses'))
   .processor(require('./processors/matchUpDirectiveDecorators'))
+  .processor(require('./processors/addMetadataAliases'))
   .processor(require('./processors/filterContainedDocs'))
   .processor(require('./processors/markBarredODocsAsPrivate'))
   .processor(require('./processors/filterPrivateDocs'))