Port MASTG-TEST-0052: Testing Local Data Storage (ios) (by @guardsquare)

[serek8]

This PR closes #2929.

I split this test into 3:

• Filesystem Content comparison => MASWE-0006
• Static search for APIs => MASWE-0006
• Keychain Security Policies => MASWE-0008

[cpholguera]

This test still has something fundamental that we need to capture in a new test (or two): the app uses the Keychain API in 2 ways

• to store data in the Keychain itself (the keychain wasn't designed for this but developers do it)
• to encrypt data using keys from the Keychain and store it in private storage (envelope encryption)

[cpholguera]

I think we should add the use of encryption APIs for envelope encryption or the explicit use of insecure data protection classes (?)

[serek8]

I am not sure I understand

[cpholguera]

We need to add here any references to encryption APIs so that the tester has everything they need.

See below in "Evaluation": we address now the "writing files" part but not the "unencrypted" part.

If we have both, then the rev. engineer can go and reverse the files and validate.

[cpholguera]

This would be L1: https://developer.apple.com/documentation/uikit/encrypting-your-app-s-files

And for L2 we'd actually encrypt the files with a key from the Keychain