Resolves https://github.com/microsoft/playwright-mcp/issues/31.
Prompt used for testing:
```
upload test.txt to dropbox
```
This won't work for asynchronously opened filechoosers, but let's start
with the synchronous variant. I also tested with including the file
chooser open state in the snapshot, but that didn't give better results.
I also tested with OneDrive and WeTransfer, but somehow our ARIA
snapshots for those pages are missing some elements that are crucial to
locate the upload buttons.
