Make engine reconnection test pass every time (#3066)

* Ensure that isFreezeFrame is reset by isFirstRender, because it can't be a freeze frame if it's the first render

* `restart`-type engine starts should count as first renders

* Ensure we don't see a loading spinner after network is reconnected in test

* Make `waitForPageLoad` robust against if the page has already loaded
and make it actually wait for the Start Sketch button to be enabled

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Co-authored-by: 49fl <ircsurfer33@gmail.com>

e2e/playwright/flow-tests.spec.ts

@@ -7221,6 +7221,7 @@ test.describe('Test network and connection issues', () => {
 
     // Expect the network to be up
     await expect(page.getByText('Network Health (Connected)')).toBeVisible()
+    await expect(page.getByTestId('loading-stream')).not.toBeAttached()
 
     // Click off the code pane.
     await page.mouse.click(100, 100)