Fix remaining file picker issues

[mathiasbynens]

When https://chromium-review.googlesource.com/c/chromium/src/+/1935410 landed upstream, we made some changes to the way Puppeteer deals with file uploads:

• fix: prepare jsHandle.uploadFile for CDP Page.handleFileChooser removal #5196 attempted to avoid the use of DOM.setFileInputFiles (but it turns out we can continue relying on it, so we should investigate undoing these changes in favor of DOM.setFileInputFiles)
• 013a86c updated FileChooser accordingly
• fix(filechooser): quick fix for the headful file chooser #5369 was needed to restore the headful file chooser functionality
• Emit change event on uploadFile calls #5389 restored the old change event behavior

Even after those follow-up fixes, there are still remaining issues with the file picker. We should investigate these open issues, close the ones that are fixed, add tests for the remaining issues and resolve them.