fix(iOSmacOS): Obsolete the use of readonly fields

[spouliot]

GitHub Issue (If applicable): closes #9027

PR Type

What kind of change does this PR introduce?

• Bugfix

What is the current behavior?

ViewHelper has C# readonly fields for MainScreenScale and IsRetinaDisplay that are evaluated only once. IOW they are set to the current screen when the evaluation is done and moving the window to a different screen will not update the values.

What is the new behavior?

Both readonly fields are now decorated with [Obsolete] attributes giving update instructions to directly use (now cached) DisplayInformation properties. This ensure the current (screen) values will be given for every call during the app lifetime.

PR Checklist

Please check if your PR fulfills the following requirements:

• Docs have been added/updated which fit documentation template (for bug fixes / features)
• Unit Tests and/or UI Tests for the changes have been added (for bug fixes / features) (if applicable)
• Validated PR Screenshots Compare Test Run results.
• Contains NO breaking changes
• Associated with an issue (GitHub or internal) and uses the automatic close keywords.
• Commits must be following the Conventional Commits specification.

Other information

Internal Issue (If applicable):

[gitpod-io]

[jeromelaban]

Nice ! Let's validate the screenshot comparison results as well.

[jeromelaban]

Screenshots look good!