[meta] use npmignore to autogenerate an npmignore file

Author: ljharb

.gitignore

@@ -9,3 +9,5 @@ yarn.lock
 # Coverage
 coverage
 .nyc_output
+
+.npmignore

.npmignore

@@ -17,12 +17,14 @@
     "has-tostringtag": "^1.0.0",
     "make-arrow-function": "^1.2.0",
     "mock-property": "^1.0.0",
+    "npmignore": "^0.3.0",
     "nyc": "^10.3.2",
     "safe-publish-latest": "^2.0.0",
     "string.prototype.repeat": "^1.0.0",
     "tape": "^5.5.3"
   },
   "scripts": {
+    "prepack": "npmignore --auto --commentLines=autogenerated",
     "prepublish": "not-in-publish || npm run prepublishOnly",
     "prepublishOnly": "safe-publish-latest",
     "pretest": "npm run lint",
@@ -81,5 +83,11 @@
     "commitLimit": false,
     "backfillLimit": false,
     "hideCredit": true
+  },
+  "publishConfig": {
+    "ignore": [
+      ".github/workflows",
+      "./test-core-js.js"
+    ]
   }
 }