Update core to use new Webpack config, flarum-tsconfig, and build action (#2856)

* Update core to use new Webpack and TSConfig

* Bump webpack dep

* Update JS build action

* Copy custom `.d.ts` files to `dist-typings` folder on typings compile

* Run workflow against action v2

This allows us to have a moving tag, like first party actions have.

* Remove bundle analyzer from core

* Use webpack config 0.1.0-beta.16.2

* Add note about checking flarum-tsconfig

.github/workflows/build.yml

@@ -22,9 +22,12 @@ jobs:
           restore-keys: |
             ${{ runner.os }}-node-
 
-      # Our action will install npm, cd into `./js`, run `npm run build`,
-      # then commit and upload any changes
+      # Our action will install npm, cd into `./js`, run `npm run build` and
+      # `npm run build-typings`, then commit and upload any changes
       - name: Build production JS
-        uses: flarum/action-build@master
-        env:
-          GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
+        uses: flarum/action-build@2
+        with:
+          github_token: ${{ secrets.GITHUB_TOKEN }}
+          build_script: build
+          package_manager: npm
+          typings_script: build-typings