refactor: improve and consolidate interfaces

[vbreuss]

Make the following changes for the interfaces:

1. Enable Nullable reference types
2. Improve and cleanup XML documentation and sort properties and methods in interfaces alphabetically
3. Consolidate the naming in the factory methods to always use just New; so instead of new DirectoryInfo(path) you should use IFileSystem.DirectoryInfo.New(path). The previous existing factory methods were kept and marked as Obsolete.
4. Added a Wrap method to the factory interfaces that can be used instead of a direct cast (which is not possible for interfaces) to create a wrapped interface from a "System.IO" type.
5. Removed the WriteAllLinesAsync with array overload, as it is not defined in System.IO and overload resolution will automatically use the IEnumerable overload.
6. Added missing methods: ResolveLinkTarget and CreateAsSymbolicLink
7. Change the return type for Stream-Methods to a custom defined FileSystemStream.
   Note: This should fix the issues from feat: Add Name to IFile.Create (and others) #793 , right?

Added the following extensibility measures:

• Add IFileSystem FileSystem property to more classes to enable implementing extension methods.
  This was simplified by adding a base interface IFileSystemExtensionPoint
• Add a IFileSystemExtensibility Extensibility property on IFileSystemInfo and IFileSystemStream which grants access to the underlying wrapped instance or to a metadata dictionary to store additional information together with the instance.

[vbreuss]

@fgreinacher :
I tried to refactor (especially the interfaces). Is this the correct approach that you envisioned?

[vbreuss]

@fgreinacher :
Did you have time to have a look at this PR?
If this is through, I plan to add two further updates, but in separate PRs:

1. Extract the ACL-related method to extension methods in TestableIO.System.IO.Abstractions.Wrappers
2. Add support for the new methods introduced in .NET 7

[fgreinacher]

@fgreinacher : Did you have time to have a look at this PR? If this is through, I plan to add two further updates, but in separate PRs:

1. Extract the ACL-related method to extension methods in TestableIO.System.IO.Abstractions.Wrappers
2. Add support for the new methods introduced in .NET 7

Sorry @vbreuss, I'll have a look today!

[fgreinacher]

Thanks a lot @vbreuss, this looks great, I left some suggestions/questions!

[vbreuss]

Thanks for the review, @fgreinacher !

I implemented all review findings and answered your questions :-)
Could you please ignore the Codacy-Issue, as I can't remove the partial from IFile (seems like a false positive)?

Are the next planned steps also OK for you?

1. Extract the ACL-related method to extension methods in TestableIO.System.IO.Abstractions.Wrappers
2. Add support for the new methods introduced in .NET 7
3. Re-Implement the "ResolveLinkTarget" functionality

[fgreinacher]

Thanks again for your hard work here!

The next steps are also fine from my side 👍

[vbreuss]

@fgreinacher :
It seems Codacy didn't trigger a new scan.

Pull Request Scan

Is there anything I can do?

[fgreinacher]

@fgreinacher : It seems Codacy didn't trigger a new scan.

Pull Request Scan

Is there anything I can do?

All good, sometimes it just takes a bit 🐌