File instrumentation - missing functions

[kahest]

Description

There are some functions that should be captured by auto instrumentation but currently aren't, maybe due to API/impl changes in Swift/iOS:

• string.write(to: filePath, atomically: true, encoding: .utf8)
  • workaround: string.data(using: .utf8)?.write(to: filePath)
• String(contentsOf: url)
• more TBD

[philipphofmann]

Let's check if we can swizzle these methods above. If we can, let's swizzle them. If not, don't put much effort into making them available.

Please also update the docs.