Prepare repository for gradual flow->ts migration (#12317)

Co-authored-by: Bogdan Savluk <savluk.bogdan@gmail.com>

package.json

@@ -27,6 +27,7 @@
     "@babel/plugin-transform-runtime": "^7.12.0",
     "@babel/preset-env": "^7.12.0",
     "@babel/preset-flow": "^7.10.4",
+    "@babel/preset-typescript": "^7.12.1",
     "@babel/register": "^7.12.0",
     "@babel/runtime": "^7.12.0",
     "@rollup/plugin-babel": "^5.2.0",
@@ -34,6 +35,8 @@
     "@rollup/plugin-json": "^4.1.0",
     "@rollup/plugin-node-resolve": "^9.0.0",
     "@rollup/plugin-replace": "^2.3.3",
+    "@typescript-eslint/eslint-plugin": "^4.6.1",
+    "@typescript-eslint/parser": "^4.6.1",
     "babel-plugin-transform-charcodes": "^0.2.0",
     "chalk": "^2.4.2",
     "charcodes": "^0.2.0",
@@ -61,7 +64,7 @@
     "rollup-plugin-terser": "^7.0.0",
     "test262-stream": "^1.3.0",
     "through2": "^2.0.0",
-    "typescript": "^3.6.3"
+    "typescript": "^4.0.5"
   },
   "workspaces": [
     "codemods/*",
@@ -78,7 +81,7 @@
     "yarn": ">=1.4.0"
   },
   "lint-staged": {
-    "*.js": [
+    "*.{js,ts}": [
       "eslint --format=codeframe"
     ]
   },