Port MASTG-TEST-0073: Testing UIPasteboard (ios) (by @guardsquare)

[pascalj]

This PR closes #2966

This pull request introduces significant updates related to monitoring and testing the use of the iOS general pasteboard. It includes the addition of new technical guidance, test cases, and the deprecation of an older test in favor of a more detailed and structured approach. Key changes are grouped into technical guidance, new test cases, and deprecation updates:

Technical Guidance:

• Added a new document MASTG-TECH-0134.md that provides comprehensive instructions on monitoring the iOS pasteboard for sensitive data, including methods to retrieve pasteboard information, detect sensitive data, and build a custom pasteboard monitor.

New Test Cases:

• Introduced MASTG-TEST-0276.md for static analysis of the iOS general pasteboard to ensure sensitive data is not written to it.
• Added MASTG-TEST-0277.md for dynamic analysis to monitor sensitive data being written to the pasteboard at runtime.
• Created draft tests:
  • MASTG-TEST-0278.md to verify that pasteboard contents are cleared when the app moves to the background or terminates.
  • MASTG-TEST-0279.md to ensure pasteboard contents have an expiration date.
  • MASTG-TEST-0280.md to check if pasteboard contents are restricted to the local device.

Deprecation Updates:

• Deprecated MASTG-TEST-0073.md with a note pointing to the new test cases in MASTG V2. Updated its content to reference MASTG-TECH-0134 for runtime pasteboard monitoring and removed redundant technical details. [1] [2] [3]

[pascalj]

A couple of comments:

• Persistence is handled automatically with iOS 10.0, i.e. if you have sensitive data just don't add it to the generalPasteboard. All app-specific pasteboards are not persistent.
• Handoff is handled securely and locally (BLE and Wifi like Airdrop), so I think it doesn't pose an additional risk.
• Since iOS 14 the user must show intent to allow apps to read from the pasteboard which makes this only a risk when you consider user error as a threat.