mac-virtualcam: Update NotInstalled error text for macOS 15

[jcm93]

Description

Updates the error message for an uninstalled/not-yet-approved camera system extension on macOS 15.

Motivation and Context

Apple moved where the user approves system extensions away from "Privacy & Security" to "General -> Login Items & Extensions". Don't want to provide outdated/incorrect directions. Beta users have already arrived confused in support about the old message.

How Has This Been Tested?

Tested in an offline branch with a custom signing configuration to allow for the installation of system extensions, then relevant changes manually copied to this branch but not technically tested. Should be double checked.

Types of changes

• Bug fix (non-breaking change which fixes an issue)

Checklist:

• My code has been run through clang-format.
• I have read the contributing document.
• My code is not on the master branch.
• The code has been tested.
• All commit messages are properly formatted and commits squashed where appropriate.
• I have included updates to all appropriate documentation.

[PatTheMav]

Should be fine.

On the whole I'd rather present a dialog box with a specific button that will take you to the corresponding settings dialog instead of using a breadcrumb string which is not particularly easy to parse.