Add support for C# 14.0 features

New language features: (See [What's new in C# 14](https://learn.microsoft.com/en-us/dotnet/csharp/whats-new/csharp-14))

- [ ] Extension members
  - [ ] Tests added
- [ ] Null-conditional assignment
  - [ ] Tests added
- [ ] field backed properties
  - [ ] Tests added
- [ ] More partial members
  - [ ] Tests added
- [ ] User defined compound assignment
  - [ ] Tests added