feat: frontend Model extender (#3646)

* feat: reintroduce frontend extenders
* chore: used `Routes` extender in bundled extensions
* chore: used `PostTypes` extender in bundled extensions
* chore: `yarn format`
* feat: `Model` frontend extender
* chore: naming
* chore(review): attributes can be nullable or undefined
* chore(review): delay extender implementation
* chore(review): unnecessary check
* chore(review): stay consistent
* chore: merge conflicts
* chore: unused import
* chore: multiline extenders
* feat: add Store extender

Signed-off-by: Sami Mazouz <sychocouldy@gmail.com>

extensions/suspend/js/tsconfig.json

@@ -0,0 +1,20 @@
+{
+  // Use Flarum's tsconfig as a starting point
+  "extends": "flarum-tsconfig",
+  // This will match all .ts, .tsx, .d.ts, .js, .jsx files in your `src` folder
+  // and also tells your Typescript server to read core's global typings for
+  // access to `dayjs` and `$` in the global namespace.
+  "include": ["src/**/*", "../../../framework/core/js/dist-typings/@types/**/*", "@types/**/*"],
+  "compilerOptions": {
+    // This will output typings to `dist-typings`
+    "declarationDir": "./dist-typings",
+    "paths": {
+      "flarum/*": ["../../../framework/core/js/dist-typings/*"],
+      // TODO: remove after export registry system implemented
+      // Without this, the old-style `@flarum/core` import is resolved to
+      // source code in flarum/core instead of the dist typings.
+      // This causes an inaccurate "duplicate export" error.
+      "@flarum/core/*": ["../../../framework/core/js/dist-typings/*"],
+    }
+  }
+}