Fix(NewMessage): Clear main message input when upload editor is open

[DorraJaouad]

☑️ Resolves

Main chat input stays empty when upload editor is open.

🖌️ UI Checklist

🖼️ Screenshots / Screencasts

🏚️ Before	🏡 After

🏁 Checklist

• 🌏 Tested with Chrome, Firefox and Safari or should not be risky to browser differences
• 🖥️ Tested with Desktop client or should not be risky for it
• 🖌️ Design was reviewed, approved or inspired by the design team
• ⛑️ Tests are included or not possible
• 📗 User documentation in https://github.com/nextcloud/documentation/tree/master/user_manual/talk has been updated or is not required

[nickvergessen]

Random thought, instead of clearing it, could we "hide" it? :P

[Antreesy]

instead of clearing it, could we "hide" it? :P

Opacity applies only partly (wouldn't work here for text nodes), and some guards from the PR are nice to have to prevent some side computations

[DorraJaouad]

Random thought, instead of clearing it, could we "hide" it? :P

It will use some invisible computations that we don't need.