Add c-sharp textobjects

[gbogarinb]

This PR adds basic textobjext based navigation for c-sharp.

[the-mikedavis]

Jumping around in some C# files I have locally, I think we should also have function textobjects for property definitions like:

public override bool CanRead {
	get { return true; }
}

But I'm not sure if we should tag the entire property as function.around (the property_declaration node) or just the accessor declaration (accessor_declaration node)

Also constructor definitions:

public BufferPoolStream(BufferPool bufferPool) {
	if (bufferPool == null)
		throw new ArgumentNullException("bufferPool");
	_bufferPool = bufferPool;
}

(constructor_declaration body: (_) @function.inside) @function.around

[gbogarinb]

Do you think it would be appropriate to map it like this until we have more precise navigation commands?

([
  (class_declaration body: (_) @class.inside)
  (struct_declaration body: (_) @class.inside)
  (interface_declaration body: (_) @class.inside)
  (enum_declaration body: (_) @class.inside)
  (delegate_declaration)
  (record_declaration body: (_) @class.inside)
  (record_struct_declaration body: (_) @class.inside)
  ]) @class.around

Note: To make record_struct_declaration work the grammar revision has to be updated along with its highlights.scm.

About property_declaration vs accessor_declaration, playing around, (property_declaration (_) @function.inside) @function.around feels more consistent with the rest of the commands, specially when using it with match inside/around function (mif, maf).

Class for testing.

namespace NavigationTest {
	public class ClassTest {
		public int field = 0;
		
		public int Field {
			get { return field; }
			set { field = value; }
		}

		public NavigationTest(string param1, int param2) {
			// Set field.
			field = param2;
		}

		~NavigationTest() {
		}

		/// Documentation.
		///
		/// Documentation.
		public int Method(string param1, int param2) {
			/* Multiline
				comment.
			*/
			return 0;
		}
	}
	
	public enum EnumTest {
		Item1,
		Item2
	}
	
	public interface InterfaceTest {
		public void Method();
	}
	
	public struct StructTest {
		public int field = 0;
	}

	public record RecordTest {
		public int field = 0;
	}

	public record struct RecordStructTest {
		public int field = 0;
	}
}

Let me know what you think.

[the-mikedavis]

Looks great, thank you!