Use alias classes instead of alias references

Conditionally define VSGitExt14, VSGitExt15 and VSGitExt16 to avoid
having to use reference aliases.

Author: jcansdale

src/GitHub.TeamFoundation.14/Services/VSGitExt.cs

@@ -15,6 +15,24 @@
 
 namespace GitHub.VisualStudio.Base
 {
+    // This is a workaround to avoid using reference aliases, which don't currently work with <PackageReference>.
+#if TEAMEXPLORER14
+    public class VSGitExt14 : VSGitExt
+    {
+        public VSGitExt14(IServiceProvider serviceProvider, IGitService gitService) : base(serviceProvider, gitService) { }
+    }
+#elif TEAMEXPLORER15
+    public class VSGitExt15 : VSGitExt
+    {
+        public VSGitExt15(IServiceProvider serviceProvider, IGitService gitService) : base(serviceProvider, gitService) { }
+    }
+#elif TEAMEXPLORER16
+    public class VSGitExt16 : VSGitExt
+    {
+        public VSGitExt16(IServiceProvider serviceProvider, IGitService gitService) : base(serviceProvider, gitService) { }
+    }
+#endif
+
     /// <summary>
     /// This service acts as an always available version of <see cref="IGitExt"/>.
     /// </summary>

src/GitHub.VisualStudio/GitHub.VisualStudio.csproj

@@ -605,22 +605,22 @@
       <Private>True</Private>
       <IncludeOutputGroupsInVSIX>BuiltProjectOutputGroup;GetCopyToOutputDirectoryItems;DebugSymbolsProjectOutputGroup;</IncludeOutputGroupsInVSIX>
       <IncludeOutputGroupsInVSIXLocalOnly>DebugSymbolsProjectOutputGroup;</IncludeOutputGroupsInVSIXLocalOnly>
-      <Aliases>TF14</Aliases>
+      <Aliases>global</Aliases>
     </ProjectReference>
     <ProjectReference Include="..\GitHub.TeamFoundation.15\GitHub.TeamFoundation.15.csproj">
       <Project>{161dbf01-1dbf-4b00-8551-c5c00f26720e}</Project>
       <Name>GitHub.TeamFoundation.15</Name>
       <Private>True</Private>
       <IncludeOutputGroupsInVSIX>BuiltProjectOutputGroup;GetCopyToOutputDirectoryItems;DebugSymbolsProjectOutputGroup;</IncludeOutputGroupsInVSIX>
       <IncludeOutputGroupsInVSIXLocalOnly>DebugSymbolsProjectOutputGroup;</IncludeOutputGroupsInVSIXLocalOnly>
-      <Aliases>TF15</Aliases>
+      <Aliases>global</Aliases>
     </ProjectReference>
     <ProjectReference Include="..\GitHub.TeamFoundation.16\GitHub.TeamFoundation.16.csproj">
       <Project>{F08BD4BC-B5DF-4193-9B01-6D0BBE101BD7}</Project>
       <Name>GitHub.TeamFoundation.16</Name>
       <IncludeOutputGroupsInVSIX>BuiltProjectOutputGroup;GetCopyToOutputDirectoryItems;DebugSymbolsProjectOutputGroup;</IncludeOutputGroupsInVSIX>
       <IncludeOutputGroupsInVSIXLocalOnly>DebugSymbolsProjectOutputGroup;</IncludeOutputGroupsInVSIXLocalOnly>
-      <Aliases>TF16</Aliases>
+      <Aliases>global</Aliases>
     </ProjectReference>
     <ProjectReference Include="..\GitHub.UI.Reactive\GitHub.UI.Reactive.csproj">
       <Project>{158b05e8-fdbc-4d71-b871-c96e28d5adf5}</Project>

src/GitHub.VisualStudio/Services/VSGitExtFactory.cs

@@ -1,13 +1,7 @@
-extern alias TF14;
-extern alias TF15;
-extern alias TF16;
-
-using System;
+using System;
 using GitHub.Logging;
+using GitHub.VisualStudio.Base;
 using Serilog;
-using VSGitExt14 = TF14.GitHub.VisualStudio.Base.VSGitExt;
-using VSGitExt15 = TF15.GitHub.VisualStudio.Base.VSGitExt;
-using VSGitExt16 = TF16.GitHub.VisualStudio.Base.VSGitExt;
 
 namespace GitHub.Services
 {