Add rollup-plugin-terser as a dev dependency:

- Fix rails#54795
- This dependency is missing from Action Text. We should require
  it explicitely instead of relying on the fact that it's
  a transitive dependency from Active Storage.

Author: Edouard-chin

actiontext/package.json

@@ -31,6 +31,7 @@
     "@rollup/plugin-commonjs": "^19.0.1",
     "@rollup/plugin-node-resolve": "^11.0.1",
     "rollup": "^2.35.1",
+    "rollup-plugin-terser": "^7.0.2",
     "trix": "^2.0.0"
   },
   "scripts": {