Using the UserAgent string for detecting the platform is deprecated by Chrome

[susnux]

Describe the bug From #2762 (comment) related to this code: https://github.com/nextcloud/text/blob/a84d082de3ce888ffe7b68c764bddbf2ff45a193/src/components/Menu/keys.js#L1

navigator.platform is deprecated but using the user agent string is also deprecated by Chrome. The future way of handling user agent related things is to use user agent client hints.

Currently client hints are not widely (currently missing Firefox and Safari) implemented, so this is bug is a reminder for possible future compatibility problems with chrome.