test(e2e): wait for the start-up splash in the workbench fixture

The splash covers the page and swallows raw mouse presses until it has faded
out. Only one spec waited for it, so the tool window resize test sometimes
pressed on the splash instead of the gap (3 of 15 runs locally). The workbench
fixture now waits for it to be removed.

e2e/fixtures.ts

@@ -16,6 +16,8 @@ export const test = base.extend<{ workbench: Page }>({
     await page.goto("/");
     await expect(page.getByRole("tree", { name: "Project" })).toBeVisible();
     await expect(page.getByRole("treeitem", { name: /acme-api/ })).toBeVisible();
+    // The start-up splash swallows raw mouse presses until it has faded out.
+    await expect(page.locator("#splash")).toHaveCount(0);
     await provide(page);
     expect(errors, "uncaught page errors").toEqual([]);
   },

e2e/projectTree.spec.ts

@@ -78,8 +78,6 @@ const settle = (page: Page) =>
   page.evaluate(() => new Promise((done) => requestAnimationFrame(() => requestAnimationFrame(done))));
 
 async function fileRow(page: Page) {
-  // The start-up splash swallows raw mouse presses until it has faded out.
-  await expect(page.locator("#splash")).toHaveCount(0);
   const file = page.getByRole("tree", { name: "Project" }).getByRole("treeitem", { name: "settings.gradle.kts" });
   await file.scrollIntoViewIfNeeded();
   const content = file.locator("[data-project-path]");