revert: perf: remove src directory from npm module (#6072)

adding src dir back to npm package because projects that create
custom renderers (e.g. nativescript-vue) relie on it.

package.json

@@ -7,6 +7,7 @@
   "unpkg": "dist/vue.js",
   "typings": "types/index.d.ts",
   "files": [
+    "src",
     "dist/*.js",
     "types/*.d.ts"
   ],