Add watchman hard reset script

- favour `watch-del-all` over only current dir `watch-del .` for nuke/hard reset
- favour logical && vs POSIX-only semi
  - for windows (cmd.exe) compat
  - always fail if either commands fail

Author: leotm

package.json

@@ -7,6 +7,7 @@
     "allow:auto": "allow-scripts auto",
     "start": "react-native start",
     "start:reset": "react-native start --reset-cache",
+    "watchman:reset": "watchman watch-del-all && watchman shutdown-server",
     "android": "react-native run-android --active-arch-only",
     "android:release": "react-native run-android --active-arch-only --variant release",
     "ios": "react-native run-ios",