This is a speculative fix that moves "background pages cleanup"
to `_didCloseInternal` so that it is only run once, but on both
context closure and browser closure.
Symptom from a flaky test:
```log
browserContext.close: page@18087c372d32819222707ca5e8fd1030 is sending "close" event after being disposed
at PageDispatcher._dispatchEvent (D:\a\playwright\playwright\src\dispatchers\dispatcher.ts:86:15)
at Page.<anonymous> (D:\a\playwright\playwright\src\dispatchers\pageDispatcher.ts:59:12)
at Page.emit (events.js:314:20)
at Page._didClose (D:\a\playwright\playwright\src\server\page.ts:220:10)
at CRPage.didClose (D:\a\playwright\playwright\src\server\chromium\crPage.ts:165:16)
at CRBrowserContext._onClosePersistent (D:\a\playwright\playwright\src\server\chromium\crBrowser.ts:476:24)
at CRBrowserContext.close (D:\a\playwright\playwright\src\server\browserContext.ts:288:20)
```
Consider the following sequence:
- page opens a popup;
- popup target is attached, we start initializing it;
- user calls browser.close();
- browser is closed, and popup initialization fails;
- we report "errored page" on the already closed context;
- RPC client cannot make sense of this:
"Cannot find parent object BrowserContext@guid to create Frame@guid"
This issue was revealed during Firefox pipe migration.
- This leaves just `recordVideos` and `videoSize` options on the context.
- Videos are saved to `artifactsPath`. We also save their ids to trace.
- `context.close()` waits for the processed videos.
