Specify inert as hidden behind the flag (#6323)
Specify inert as hidden behind the flag (#6323)

- EdgeHTML didn't support it: https://developer.microsoft.com/en-us/microsoft-edge/status/inertattribute/?q=inert
- new Edge mirrors from Chrome
- Operas mirror from Chrome
- Samsung Internet doesn't do flags
- WebView doesn't do flags

Co-authored-by: Daniel D. Beck <3d0f3b9ddcacec30c4008c5e030e6c13a478cb4f@ddbeck.com>
mdn/browser-compat-data,chrisdavidmills/browser-compat-data,mdn/browser-compat-data,chrisdavidmills/browser-compat-data