(core) repair grist-ee build and add smoke test

Summary:
This fixes the grist-ee build after recent changes, by
giving it a stub for ProductUpgrades.ts. Extends the
`core` test to also check if `ext` variant builds, to
catch the most common form of breakage on grist-ee so
far (file organization).

Test Plan: extends test

Reviewers: georgegevoian

Reviewed By: georgegevoian

Differential Revision: https://phab.getgrist.com/D3484

app/client/ui/ProductUpgradesStub.ts

@@ -0,0 +1,27 @@
+import type {AppModel} from 'app/client/models/AppModel';
+import {commonUrls} from 'app/common/gristUrls';
+import {Disposable} from 'grainjs';
+
+export function buildUpgradeNudge(options: {
+  onClose: () => void;
+  onUpgrade: () => void
+}) {
+  return null;
+}
+
+export function buildNewSiteModal(owner: Disposable, current: string | null) {
+  window.location.href = commonUrls.plans;
+}
+
+export function buildUpgradeModal(owner: Disposable, planName: string)  {
+  window.location.href = commonUrls.plans;
+}
+
+export class UpgradeButton extends Disposable {
+  constructor(appModel: AppModel) {
+    super();
+  }
+  public buildDom() {
+    return null;
+  }
+}

stubs/app/client/ui/ProductUpgrades.ts

@@ -1,27 +1 @@
-import type {AppModel} from 'app/client/models/AppModel';
+export * from 'app/client/ui/ProductUpgradesStub';
-import {commonUrls} from 'app/common/gristUrls';
-import {Disposable} from 'grainjs';
-
-export function buildUpgradeNudge(options: {
-  onClose: () => void;
-  onUpgrade: () => void
-}) {
-  return null;
-}
-
-export function buildNewSiteModal(owner: Disposable, current: string | null) {
-  window.location.href = commonUrls.plans;
-}
-
-export function buildUpgradeModal(owner: Disposable, planName: string)  {
-  window.location.href = commonUrls.plans;
-}
-
-export class UpgradeButton extends Disposable {
-  constructor(appModel: AppModel) {
-    super();
-  }
-  public buildDom() {
-    return null;
-  }
-}