ci: support TS type-checking in CI

- add `yarn tscheck` command
  - same naming as Babel core

- modify `yarn validate` to also run `yarn tscheck`

- modify ci.yml GitHub workflow to also run `yarn tscheck`

- add `yarn tscheck` to CONTRIBUTING.md

.github/workflows/ci.yml

@@ -52,6 +52,8 @@ jobs:
         run: yarn lint
       - name: Flow
         run: yarn flow
+      - name: TSCheck
+        run: yarn tscheck
       - name: Check compat-data
         run: yarn build-es-shims-data
         env:

CONTRIBUTING.md

@@ -40,10 +40,18 @@ $ yarn lint
 
 #### Type-check
 
+To run Flow type-checking, run:
+
 ```sh
 $ yarn flow
 ```
 
+To run TypeScript type-checking, run:
+
+```sh
+$ yarn tscheck
+```
+
 #### Test
 
 ```sh

package.json

@@ -13,7 +13,8 @@
     "publish": "yarn clean && NODE_ENV=production yarn build && yarn validate && lerna publish from-git",
     "test": "jest && yarn test:esm",
     "test:esm": "node test/esm/index.mjs",
-    "validate": "yarn lint && yarn flow && yarn test",
+    "tscheck": "yarn tsc",
+    "validate": "yarn lint && yarn flow && yarn tscheck && yarn test",
     "watch": "gulp watch"
   },
   "devDependencies": {