Move the code related to plugin loading / installation to "flipper-plugin-lib"

Summary:
Sorry for so long diff, but actually there are no functional changes, just refactoring to make further changes of Plugin Manager easier to understand.

I've de-coupled the code related to plugin management from UI code and moved it from PluginInstaller UI component (which will be replaced soon by new UI) to "flipper-plugin-lib".  So pretty much everything related to plugin discovery and installation now consolidated in this package.

Additionally, this refactoring enables re-using of plugin management code in "flipper-pkg", e.g. to create CLI command for plugin installation from NPM, e.g.: `flipper-pkg install flipper-plugin-reactotron`.

Reviewed By: passy

Differential Revision: D23679346

fbshipit-source-id: 82e7b9de9afa08c508c1b228c2038b4ba423571c

desktop/plugin-lib/src/getNpmHostedPlugins.ts

@@ -0,0 +1,46 @@
+/**
+ * Copyright (c) Facebook, Inc. and its affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ *
+ * @format
+ */
+
+import {default as algoliasearch, SearchIndex} from 'algoliasearch';
+
+const ALGOLIA_APPLICATION_ID = 'OFCNCOG2CU';
+const ALGOLIA_API_KEY = 'f54e21fa3a2a0160595bb058179bfb1e';
+
+function provideSearchIndex(): SearchIndex {
+  const client = algoliasearch(ALGOLIA_APPLICATION_ID, ALGOLIA_API_KEY);
+  return client.initIndex('npm-search');
+}
+
+export type NpmPackageDescriptor = {
+  name: string;
+  version: string;
+};
+
+export type NpmHostedPluginsSearchArgs = {
+  query?: string;
+};
+
+export async function getNpmHostedPlugins(
+  args: NpmHostedPluginsSearchArgs = {},
+): Promise<NpmPackageDescriptor[]> {
+  const index = provideSearchIndex();
+  args = Object.assign(
+    {
+      query: '',
+      filters: 'keywords:flipper-plugin',
+      hitsPerPage: 50,
+    },
+    args,
+  );
+  const {hits} = await index.search<NpmPackageDescriptor>(
+    args.query || '',
+    args,
+  );
+  return hits;
+}