Resolve URL path for versioned webjar directories

Prior to this commit, the `resolveUrlPath` implementation for the
`LiteWebJarsResourceResolver` would always delegate to the resource
chain once the versioned webjar folder has been resolved.

While this aligns with the `ResourceResolver` contract and the fact that
the resource chain does not resolve directories, here the WebJar locator
does support such use cases and we shouldn't get in the way here.

This commit falls back to the resolved versioned WebJar path if no
resource could be resolved and the path ends with "/".

Fixes gh-36726