fix(catalyst): Fix content behind titlebar

[dpogue]

Platforms affected

macOS Catalyst

Motivation and Context

Closes GH-1491.

Description

When showing a webview on macOS Catalyst, always position it below the titlebar when a titlebar is displayed. This has the side effect of making all the safe-area-inset values 0, regardless of the viewport-fit value.

Also adds a HideDesktopTitlebar preference to make the titlebar invisible on macOS Catalyst with content extending behind it. I named this in a generic way because it sounds like this should also be feasible to apply to the cordova-electron platform.

When using a preference to disable drawing the titlebar, safe-area-inset works as expected (but generally requires viewport-fit=cover to be specified).

Testing

Tested with viewport-fit=cover and viewport-fit=contain and measured the calculated safe-area-inset-top value.

Checklist

• I've run the tests to see all new and existing tests pass
• If this Pull Request resolves an issue, I linked to the issue in the text above (and used the correct keyword to close issues using keywords)
• I've updated the documentation if necessary

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 80.84%. Comparing base (3737f51) to head (8e93a08).

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #1517   +/-   ##
=======================================
  Coverage   80.84%   80.84%           
=======================================
  Files          16       16           
  Lines        1848     1848           
=======================================
  Hits         1494     1494           
  Misses        354      354           

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[erisu]

LGTM

Tested building app with the flag set to true and false, view-port set to contain and cover, and with and without the safe-area's defined.