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/build-utils.ts

@@ -44,8 +44,8 @@ export function compileDefaultPlugins(
     skipAll
       ? []
       : [
-          path.join(__dirname, '..', 'src', 'plugins'),
-          path.join(__dirname, '..', 'src', 'fb', 'plugins'),
+          path.join(__dirname, '..', 'plugins'),
+          path.join(__dirname, '..', 'plugins', 'fb'),
         ],
     defaultPluginDir,
     {force: true, failSilently: false, recompileOnChanges: false},