Remove default features when fullstack is enabled and one platform is enabled in the default features (#3925)

* Don't enable default features when only either the server or client is enabled

packages/playwright-tests/default-features-disabled.spec.js

@@ -0,0 +1,11 @@
+// @ts-check
+const { test, expect } = require("@playwright/test");
+
+test("loads with correct features", async ({ page }) => {
+  await page.goto("http://localhost:8002");
+
+  // Expect the page to contain the pending text.
+  const main = page.locator("#main");
+  await expect(main).toContainText('server features: ["server"]');
+  await expect(main).toContainText('client features: ["web"]');
+});