Move plugins to "sonar/desktop/plugins"

Summary:
Plugins moved from "sonar/desktop/src/plugins" to "sonar/desktop/plugins".

Fixed all the paths after moving.

New "desktop" folder structure:
- `src` - Flipper desktop app JS code executing in Electron Renderer (Chrome) process.
- `static` - Flipper desktop app JS code executing in Electron Main (Node.js) process.
- `plugins` - Flipper desktop JS plugins.
- `pkg` - Flipper packaging lib and CLI tool.
- `doctor` - Flipper diagnostics lib and CLI tool.
- `scripts` - Build scripts for Flipper desktop app.
- `headless` - Headless version of Flipper desktop app.
- `headless-tests` - Integration tests running agains Flipper headless version.

Reviewed By: mweststrate

Differential Revision: D20344186

fbshipit-source-id: d020da970b2ea1e001f9061a8782bfeb54e31ba0

desktop/scripts/yarn-install.ts

@@ -18,9 +18,9 @@ const PACKAGES = [
   'static',
   'doctor',
   'pkg',
-  'src/plugins/*',
-  'src/fb/plugins/*',
-  'src/fb/plugins/layout/*',
+  'plugins/*',
+  'plugins/fb/*',
+  'plugins/fb/layout/*',
 ];
 const WINDOWS = /^win/.test(process.platform);
 const YARN_PATH =