Missing trailing backslash after pathBase when Path is empty

### Is there an existing issue for this?

- [X] I have searched the existing issues

### Describe the bug

Found a bug that backslash is missing after PathBase, if Path is empty.

### Expected Behavior
If pathBase is non empty and Path is empty, then add a trailing backslash after pathBase in the route url.

Actual url: /twci369916wu2hsws-twci369916wu2hsws.fhir.mshapis.co**m?**_type=Patient&_count=500&ct=er97f5lRTbShgbGOqaGBuaGFqbGJiZmhibmRobGZUSwAAAD%2F%2Fw%3D%3D

Expected url: /twci369916wu2hsws-twci369916wu2hsws.fhir.mshapis.com/?_type=Patient&_count=500&ct=er97f5lRTbShgbGOqaGBuaGFqbGJiZmhibmRobGZUSwAAAD%2F%2Fw%3D%3D

The issue is here https://github.com/dotnet/aspnetcore/blob/481e472ea22a53fe96f11ba001c2dd4fbdc59ed5/src/Http/Http.Extensions/src/UriHelper.cs#L36

### Steps To Reproduce

- Search URl: https://localhost:44349/twci369916wu2hsws-twci369916wu2hsws.fhir.mshapis.com/?_type=Patient&_count=500
_Host: localhost:44349, basePath: /twci369916wu2hsws-twci369916wu2hsws.fhir.mshapis.com, Path: Empty, Query parameter: _type=Patient&_count=500__
- In our implementation, we are calling AspnetCore UrlHelper.RouteUrl() to get the route url
- Further debugging, LinkGeneratorExtensions.GetPathByRouteValues -> GetPathByAddress() -> DefaultLinkGenerator.GetPathByEndpoints() -> TryProcessTemplate() fetches _pathBase_ as ""/twci369916wu2hsws-twci369916wu2hsws.fhir.mshapis.com" and _Path_ as ""(empty)
- UriHelper.BuildRelative constructs the url as below
/twci369916wu2hsws-twci369916wu2hsws.fhir.mshapis.co**m?**_type=Patient&_count=500&ct=er97f5lRTbShgbGOqaGBuaGFqbGJiZmhibmRobGZUSwAAAD%2F%2Fw%3D%3D

Expected url: /twci369916wu2hsws-twci369916wu2hsws.fhir.mshapis.com/?_type=Patient&_count=500&ct=er97f5lRTbShgbGOqaGBuaGFqbGJiZmhibmRobGZUSwAAAD%2F%2Fw%3D%3D

### Exceptions (if any)

_No response_

### .NET Version

_No response_

### Anything else?

_No response_

Start in src/Http/Http.Extensions/src/UriHelper.cs at the referenced line and trace how UriHelper.BuildRelative combines PathBase, Path, and the query string. Reproduce the empty-Path case through the reported RouteUrl flow, then verify that a non-empty PathBase produces the expected trailing slash before the query.

Written by the indexing model from the issue text.