Serialize first precision value on GeoSuggest (#4106)

Relates: #4091

This commit adds a SerializeAsSingleFormatter<T> to serialize only the first value in the Precision collection
for a GeoSuggestContext context mapping for the "completion" field data type.

Move the Context mapping related types to the Nest/Mapping/Types/Specialized/Completion directory to disambiguate
from the context query types.

Deprecate the Neighbors property on IGeoSuggestContext.

Author: russcam

src/Nest/CommonAbstractions/SerializationBehavior/JsonFormatters/SingleOrEnumerableFormatter.cs

@@ -1,4 +1,5 @@
 using System.Collections.Generic;
+using System.Linq;
 using Elasticsearch.Net.Utf8Json;
 
 namespace Nest
@@ -25,4 +26,35 @@ public void Serialize(ref JsonWriter writer, IEnumerable<T> value, IJsonFormatte
 			formatter.Serialize(ref writer, value, formatterResolver);
 		}
 	}
+
+	internal class SerializeAsSingleFormatter<T> : IJsonFormatter<IEnumerable<T>>
+	{
+		public IEnumerable<T> Deserialize(ref JsonReader reader, IJsonFormatterResolver formatterResolver)
+		{
+			var token = reader.GetCurrentJsonToken();
+			return token == JsonToken.BeginArray
+				? formatterResolver.GetFormatter<IEnumerable<T>>().Deserialize(ref reader, formatterResolver)
+				: new[] { formatterResolver.GetFormatter<T>().Deserialize(ref reader, formatterResolver) };
+		}
+
+		public void Serialize(ref JsonWriter writer, IEnumerable<T> value, IJsonFormatterResolver formatterResolver)
+		{
+			if (value == null)
+			{
+				writer.WriteNull();
+				return;
+			}
+
+			var enumerator = value.GetEnumerator();
+			if (!enumerator.MoveNext())
+			{
+				writer.WriteNull();
+				return;
+			}
+
+			var firstValue = enumerator.Current;
+			var formatter = formatterResolver.GetFormatter<T>();
+			formatter.Serialize(ref writer, firstValue, formatterResolver);
+		}
+	}
 }

src/Nest/Search/Suggesters/ContextSuggester/CategorySuggestContext.cs renamed to src/Nest/Mapping/Types/Specialized/Completion/CategorySuggestContext.cs

@@ -1,4 +1,5 @@
-using System.Collections.Generic;
+using System;
+using System.Collections.Generic;
 using System.Runtime.Serialization;
 using Elasticsearch.Net.Utf8Json;
 
@@ -7,18 +8,26 @@ namespace Nest
 	[InterfaceDataContract]
 	public interface IGeoSuggestContext : ISuggestContext
 	{
-		[DataMember(Name = "neighbors")]
+		[IgnoreDataMember]
+		[Obsolete("No longer valid. Will be removed in next major release")]
 		bool? Neighbors { get; set; }
 
+		/// <summary>
+		/// The precision of the geohash to encode the query geo point.
+		/// Only the first value will be serialized.
+		/// </summary>
+		[JsonFormatter(typeof(SerializeAsSingleFormatter<string>))]
 		[DataMember(Name = "precision")]
 		IEnumerable<string> Precision { get; set; }
 	}
 
 	[DataContract]
 	public class GeoSuggestContext : SuggestContextBase, IGeoSuggestContext
 	{
+		[Obsolete("No longer valid. Will be removed in next major release")]
 		public bool? Neighbors { get; set; }
 
+		/// <inheritdoc />
 		public IEnumerable<string> Precision { get; set; }
 		public override string Type => "geo";
 	}
@@ -29,11 +38,15 @@ public class GeoSuggestContextDescriptor<T>
 		where T : class
 	{
 		protected override string Type => "geo";
+
+		[Obsolete("No longer valid. Will be removed in next major release")]
 		bool? IGeoSuggestContext.Neighbors { get; set; }
 		IEnumerable<string> IGeoSuggestContext.Precision { get; set; }
 
+		/// <inheritdoc cref="IGeoSuggestContext.Precision" />
 		public GeoSuggestContextDescriptor<T> Precision(params string[] precisions) => Assign(precisions, (a, v) => a.Precision = v);
 
+		[Obsolete("No longer valid. Will be removed in next major release")]
 		public GeoSuggestContextDescriptor<T> Neighbors(bool? neighbors = true) => Assign(neighbors, (a, v) => a.Neighbors = v);
 	}
 }

src/Nest/Search/Suggesters/ContextSuggester/GeoSuggestContext.cs renamed to src/Nest/Mapping/Types/Specialized/Completion/GeoSuggestContext.cs

@@ -2,7 +2,6 @@
 using Elasticsearch.Net.Utf8Json;
 using Elasticsearch.Net.Utf8Json.Internal;
 
-
 namespace Nest
 {
 	internal class SuggestContextFormatter : IJsonFormatter<ISuggestContext>

src/Nest/Search/Suggesters/ContextSuggester/ISuggestContext.cs renamed to src/Nest/Mapping/Types/Specialized/Completion/ISuggestContext.cs

@@ -347,6 +347,10 @@ public static PropertiesDescriptor<TProject> ProjectProperties<TProject>(Propert
 						.Category(c => c
 							.Name("color")
 						)
+						.GeoLocation(c => c
+							.Name("geo")
+							.Precision("1")
+						)
 					)
 				)
 				.Scalar(p => p.NumberOfCommits, n => n.Store())