feat(c_sharp): add class.outer support for records, enums, interfaces

[marcinjahn]

Extends support for recognizing class.outer for the following types:

• classes with empty declarations

  public class MyClass {}

• structs with empty declarations

  public struct MyStruct {}

• records

  public record MyRecord1();
  public record MyRecord2() {}
  public record MyRecord3 {}

• interfaces

  public IMyInterface {}

• enums

  public enum MyEnum {}

Before these changes, only structs and classes (both needed to have at least 1 member) had been supported.

Closes #636

Note: Ideally, there should also be support for structs, interfaces, classes and enums without curly braces (e.g. class MyClass; or class MyClass();), but it seems that tree-sitter does not support that syntax yet, tree inspection shows errors.

[marcinjahn]

Any love for C#?