Plugin folders re-structuring

Summary:
Here I'm changing plugin repository structure to allow re-using of shared packages between both public and fb-internal plugins, and to ensure that public plugins has their own yarn.lock as this will be required to implement reproducible jobs checking plugin compatibility with released flipper versions.

Please note that there are a lot of moved files in this diff, make sure to click "Expand all" to see all that actually changed (there are not much of them actually).

New proposed structure for plugin packages:
```
- root
- node_modules - modules included into Flipper: flipper, flipper-plugin, react, antd, emotion
-- plugins
 --- node_modules - modules used by both public and fb-internal plugins (shared libs will be linked here, see D27034936)
 --- public
---- node_modules - modules used by public plugins
---- pluginA
----- node_modules - modules used by plugin A exclusively
---- pluginB
----- node_modules - modules used by plugin B exclusively
 --- fb
---- node_modules - modules used by fb-internal plugins
---- pluginC
----- node_modules - modules used by plugin C exclusively
---- pluginD
----- node_modules - modules used by plugin D exclusively
```
I've moved all public plugins under dir "plugins/public" and excluded them from root yarn workspaces. Instead, they will have their own yarn workspaces config and yarn.lock and they will use flipper modules as peer dependencies.

Reviewed By: mweststrate

Differential Revision: D27034108

fbshipit-source-id: c2310e3c5bfe7526033f51b46c0ae40199fd7586

desktop/scripts/workspaces.ts

@@ -7,7 +7,7 @@
  * @format
  */
 
-import {rootDir, pluginsDir, fbPluginsDir} from './paths';
+import {rootDir, pluginsDir, fbPluginsDir, publicPluginsDir} from './paths';
 import fs from 'fs-extra';
 import path from 'path';
 import {promisify} from 'util';
@@ -72,13 +72,15 @@ async function getWorkspacesByRoot(
 
 export async function getWorkspaces(): Promise<Workspaces> {
   const rootWorkspaces = await getWorkspacesByRoot(rootDir);
-  const fbWorkspaces = await getWorkspacesByRoot(fbPluginsDir);
-  if (!fbWorkspaces) {
-    return rootWorkspaces!;
-  }
+  const publicPluginsWorkspaces = await getWorkspacesByRoot(publicPluginsDir);
+  const fbPluginsWorkspaces = await getWorkspacesByRoot(fbPluginsDir);
   const mergedWorkspaces: Workspaces = {
     rootPackage: rootWorkspaces!.rootPackage,
-    packages: [...rootWorkspaces!.packages, ...fbWorkspaces.packages],
+    packages: [
+      ...rootWorkspaces!.packages,
+      ...publicPluginsWorkspaces!.packages,
+      ...(fbPluginsWorkspaces ? fbPluginsWorkspaces.packages : []),
+    ],
   };
   return mergedWorkspaces;
 }