Fix all remaining dependency path resolutions for source-dependencies repos

Extract GetDependenciesBaseDirectory and GetRestoredDependencyDirectory helpers
and fix all occurrences in DependenciesHelper, DependenciesConfigurationFile,
DependencySource, and RestoredArtifactsNuGetConfigGenerator.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: gfraiteur

src/PostSharp.Engineering.BuildTools/Build/Files/DependenciesConfigurationFile.cs

@@ -471,12 +471,7 @@ void WriteBuildServerSource()
 
                     case DependencySourceKind.RestoredDependency:
                         {
-                            var importProjectFile = Path.GetFullPath(
-                                Path.Combine(
-                                    context.RepoDirectory,
-                                    "dependencies",
-                                    dependency.Key,
-                                    dependency.Key + ".version.props" ) );
+                            var importProjectFile = TeamCityHelper.GetRestoredDependencyVersionFile( context.RepoDirectory, dependency.Key );
 
                             AddImport( importProjectFile );
 

src/PostSharp.Engineering.BuildTools/Build/Files/NuGet/RestoredArtifactsNuGetConfigGenerator.cs

@@ -1,6 +1,7 @@
 // Copyright (c) SharpCrafters s.r.o. See the LICENSE.md file in the root directory of this repository root for details.
 
 using PostSharp.Engineering.BuildTools.Dependencies.Model;
+using PostSharp.Engineering.BuildTools.Tools.TeamCity;
 using System.IO;
 
 namespace PostSharp.Engineering.BuildTools.Build.Files.NuGet;
@@ -36,12 +37,9 @@ protected override string GetDependencyDirectory(
         DependencyDefinition dependencyDefinition,
         BuildConfiguration configuration )
     {
-        // For restored artifacts, dependencies are always under dependencies/<name>
+        // For restored artifacts, dependencies are under the dependencies base directory
         // TeamCity artifact rule +:{PrivateArtifactsDir}/**/* => dependencies/{name} copies the contents directly
-        return Path.Combine(
-            context.RepoDirectory,
-            "dependencies",
-            dependencyKey );
+        return TeamCityHelper.GetRestoredDependencyDirectory( context.RepoDirectory, dependencyKey );
     }
 
     protected override bool ShouldIncludeDependency( DependencyDefinition dependencyDefinition )