Routing: Fix URL aliases not stored for variant content with shared alias property in DocumentUrlAliasService

[AndyButland]

Description

This fixes a bug found in testing of the document URL alias service, introduced as an optimisation for finding documents by URL alias in #21396.

I found URL aliases were not being stored for variant content types that have a shared (non-culture-varied) umbracoUrlAlias property.

The service now checks if the alias property itself varies by culture, not just the content type, which fixes this issue.

Root Cause

ExtractAliasesFromDocumentAsync only checked if the content type varies by culture. For variant content types, it always called document.GetValue<string>(alias, culture) with a culture parameter. However, for shared properties, this returns null because shared properties don't have culture-specific values.

Fix

Check if the umbracoUrlAlias property itself varies by culture:

• Invariant content type → Get value without culture ✓
• Variant content type + shared alias property → Get value without culture ✓ (fixed)
• Variant content type + variant alias property → Get value with culture ✓

Testing

For manual verification, create a variant document type with a shared, text string property with an alias of umbracoUrlAlias.
Create a document of that type, populate the property and verify it has been recorded in umbracoDocumentUrlAlias.

An integration test has been added that verifies this behaviour.

[Copilot]

Pull request overview

Fixes URL aliases not being stored for culture-variant content types when the umbracoUrlAlias property itself is shared (invariant), by checking property-level variation rather than only content-type variation.

Changes:

• Update DocumentUrlAliasService.ExtractAliasesFromDocumentAsync to read umbracoUrlAlias without culture when the property does not vary by culture (even if the content type does).
• Add integration tests covering both variant-alias and shared-alias scenarios on culture-variant content types.
• Update tests to use ITemplateService.CreateAsync instead of the obsolete IFileService.SaveTemplate.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 2 comments.

File	Description
src/Umbraco.Core/Services/DocumentUrlAliasService.cs	Determines alias culture-variance from the umbracoUrlAlias property type and stores aliases accordingly.
tests/Umbraco.Tests.Integration/Umbraco.Core/Services/DocumentUrlAliasServiceTests.cs	Adds integration test coverage for variant content types with shared vs culture-varied alias properties; updates template creation to ITemplateService.

[Zeegaan]

Looks good, tests good 🚀