build: rename 'packages' to 'workspaces'

1. This reinforces npm terminology, so it should be easier to understand
   and remember commands like: `npm i foo --workspace scratch-gui`
2. This means you can type `w<tab>` and get `workspaces`, where
   `packages` fights `package.json` and `package-lock.json` for tab
   completion.

Author: cwillisf

package-lock.json

@@ -18,7 +18,7 @@
     }
   },
   "workspaces": [
-    "packages/*"
+    "workspaces/*"
   ],
   "devDependencies": {
     "@commitlint/cli": "17.6.5",