[Static Web Assets] Fix compressed endpoint headers

[javiercn]

• When fingerprinting assets the headers were not being correctly applied to the compressed endpoints with fingerprint.
• Added a fix and a test to cover the scenario.

[javiercn]

When the token was embedded in the expression (for example, file#[.{fingerprint=value}].ext we weren't adding it to the tokens returned, so it wasn't being added as a property and we weren't setting the caching headers correctly because of that.

[javiercn]

The combination of route + asset file is unique, when we have fingerprinting expressions more than one endpoint is associated with a given compressed asset, so we need to make sure we don't add it multiple times.

Using a HashSet is simpler and better than using a list, also, in this case we need to avoid comparing using the headers and properties because those will be different.

[javiercn]

We were copying the related endpoint and applying a selector + the compressed endpoint properties. That caused for example that we created a fingerprinted endpoint using a non-fingerprinted compressed endpoint.

To address that, we check that both endpoints have or don't have fingerprint and in case of having it, they match.

This way the fingerprinted endpoint we create for content-negotiation has the same headers as the fingerprinted compressed endpoint.