Add TextDocument.GetRange(Range).

Relax some ICollection<> parameters to IEnumerable<>.

Author: CXuesong

LanguageServer.VsCode/Contracts/Command.cs

@@ -46,7 +46,7 @@ public ExecuteCommandRegistrationOptions() : this(null)
         {
         }
 
-        public ExecuteCommandRegistrationOptions(ICollection<string> commands)
+        public ExecuteCommandRegistrationOptions(IEnumerable<string> commands)
         {
             Commands = commands;
         }

LanguageServer.VsCode/Contracts/InitializationResponse.cs

@@ -259,7 +259,7 @@ public ExecuteCommandOptions()
 
         }
 
-        public ExecuteCommandOptions(IList<string> commands)
+        public ExecuteCommandOptions(IEnumerable<string> commands)
         {
             Commands = commands;
         }
@@ -268,7 +268,7 @@ public ExecuteCommandOptions(IList<string> commands)
         /// Document links have a resolve provider as well.
         /// </summary>
         [JsonProperty]
-        public IList<string> Commands { get; set; }
+        public IEnumerable<string> Commands { get; set; }
     }
 
     /// <summary>

LanguageServer.VsCode/Server/TextDocument.cs

@@ -75,6 +75,15 @@ protected virtual void OnLoad(TextDocumentItem doc)
         /// </summary>
         public abstract TextDocument ApplyChanges(IList<TextDocumentContentChangeEvent> changes);
 
+        /// <summary>
+        /// Gets a part of the content by the specified line/column-based range.
+        /// </summary>
+        public virtual string GetRange(Range range)
+        {
+            var start = OffsetAt(range.Start);
+            return GetRange(start, OffsetAt(range.End) - start);
+        }
+
         /// <summary>
         /// Gets a part of the content by the specified offset range.
         /// </summary>