Save the project file after package operation in the PM UI (#6295)

* Save the project after package installation

* Save project after uninstall

* Save legacy project references

Author: martinrrm

src/NuGet.Clients/NuGet.PackageManagement.VisualStudio/ProjectServices/VsManagedLanguagesProjectSystemServices.cs

@@ -323,6 +323,8 @@ private void AddOrUpdatePackageReference(string packageName, VersionRange packag
                 packageVersion.OriginalString ?? packageVersion.ToShortString(),
                 metadataElements,
                 metadataValues);
+
+            _vsProject4.Project.Save();
         }
 
         public async Task RemovePackageReferenceAsync(string packageName)
@@ -332,6 +334,7 @@ public async Task RemovePackageReferenceAsync(string packageName)
             await _threadingService.JoinableTaskFactory.SwitchToMainThreadAsync();
 
             _vsProject4.PackageReferences.Remove(packageName);
+            _vsProject4.Project.Save();
         }
 
         private bool IsCentralPackageManagementVersionsEnabled()

src/NuGet.Clients/NuGet.PackageManagement.VisualStudio/Projects/CpsPackageReferenceProject.cs

@@ -346,8 +346,12 @@ await SetPackagePropertyValueAsync(
                         ProjectItemProperties.IncludeAssets,
                         MSBuildStringUtility.Convert(LibraryIncludeFlagUtils.GetFlagString(installationContext.IncludeType)));
                 }
+
             }
 
+            // Save the project
+            await _unconfiguredProject.SaveAsync();
+
             return true;
         }
 
@@ -400,6 +404,10 @@ public override async Task<bool> UninstallPackageAsync(string packageId, BuildIn
 
                 await configuredProject?.Services.PackageReferences.RemoveAsync(packageId);
             }
+
+            // Save the project
+            await _unconfiguredProject.SaveAsync();
+
             return true;
         }