Fenix: FNX2-16400 ⁃ [Private Browsing] Change default PBM setting to disable screenshots

[AmyYLee]

Steps to reproduce:

Open a new tab in private browsing
Go to open apps view

Expected:
Private mode contents is hidden (for private homescreen and websites)

Actual:
Private mode contents is shown.

Rational: The idea of private browsing is that we keep your what you're looking at private except when you're actively using Private mode. Showing the contents of private browsing outside of the app (ie. open apps view) violates that.

Secondly: We should have the default set to disabled for "allow screenshots in private browsing" in private browsing settings since this is linked to the ability to hide private mode screen in the open apps view.

[mcarare]

@AmyYLee Is this same as : https://github.com/mozilla-mobile/fenix/issues/11153 + the default setting for allowing screenshots?

[AmyYLee]

@mcarare Yes it is. I was told I should open a new issue for the default toggle change.

[mcarare]

@Amy Lee, as a note, I've submitted a fix for the first part (hiding preview in private), but it does not depend on the default setting for allowing screenshots.

[ekager]

Separated out the two issues so that #11153 is tracking always hiding in the app viewer, and this can track changing the default screenshot setting to not allowed

[AndiAJ]

Hi, verified as fixed on the latest Nightly Build 200609 from 6/9 using the following devices:
• Google Pixel 3a (Android 10)
• Huawei Mate 20 Lite (Android 9)

► Video

[Mugurell]

// moving comment to another ticket.