Expose `FilePath` on `MappingLocation`.

- We had the `FilePath` information available to us but we weren't exposing it on the `MappingLocation` context object.
- By exposing the `FilePath` the Razor editor can 100% know where a `MappingLocation` is resolved from. If `null` the location is deemed to be the current source/generated file.

#552

src/Microsoft.AspNet.Razor/CodeGenerators/CSharpLineMappingWriter.cs

@@ -98,6 +98,7 @@ namespace Microsoft.AspNet.Razor.CodeGenerators
                 {
                     documentMapping = new MappingLocation(
                         location: new SourceLocation(
+                            _documentMapping.FilePath,
                             _documentMapping.AbsoluteIndex,
                             _documentMapping.LineIndex,
                             _documentMapping.CharacterIndex),

src/Microsoft.AspNet.Razor/CodeGenerators/MappingLocation.cs

@@ -1,6 +1,7 @@
 // Copyright (c) .NET Foundation. All rights reserved.
 // Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
 
+using System;
 using System.Globalization;
 using Microsoft.Extensions.Internal;
 
@@ -18,6 +19,7 @@ namespace Microsoft.AspNet.Razor.CodeGenerators
             AbsoluteIndex = location.AbsoluteIndex;
             LineIndex = location.LineIndex;
             CharacterIndex = location.CharacterIndex;
+            FilePath = location.FilePath;
         }
 
         public int ContentLength { get; }
@@ -28,6 +30,8 @@ namespace Microsoft.AspNet.Razor.CodeGenerators
 
         public int CharacterIndex { get; }
 
+        public string FilePath { get; }
+
         public override bool Equals(object obj)
         {
             var other = obj as MappingLocation;
@@ -36,7 +40,8 @@ namespace Microsoft.AspNet.Razor.CodeGenerators
                 return false;
             }
 
-            return AbsoluteIndex == other.AbsoluteIndex &&
+            return string.Equals(FilePath, other.FilePath, StringComparison.Ordinal) &&
+                AbsoluteIndex == other.AbsoluteIndex &&
                 ContentLength == other.ContentLength &&
                 LineIndex == other.LineIndex &&
                 CharacterIndex == other.CharacterIndex;
@@ -45,6 +50,7 @@ namespace Microsoft.AspNet.Razor.CodeGenerators
         public override int GetHashCode()
         {
             var hashCodeCombiner = HashCodeCombiner.Start();
+            hashCodeCombiner.Add(FilePath, StringComparer.Ordinal);
             hashCodeCombiner.Add(AbsoluteIndex);
             hashCodeCombiner.Add(ContentLength);
             hashCodeCombiner.Add(LineIndex);
@@ -56,11 +62,12 @@ namespace Microsoft.AspNet.Razor.CodeGenerators
         public override string ToString()
         {
             return string.Format(
-                CultureInfo.CurrentCulture, "({0}:{1},{2} [{3}])",
+                CultureInfo.CurrentCulture, "({0}:{1},{2} [{3}] {4})",
                 AbsoluteIndex,
                 LineIndex,
                 CharacterIndex,
-                ContentLength);
+                ContentLength,
+                FilePath);
         }
 
         public static bool operator ==(MappingLocation left, MappingLocation right)