When resolved through the `GzipResourceResolver`, CSS files can be
resolved as their pre-gzipped variant, if a ".gz" file is present in the
configured resource locations.
Such resources are gzipped and thus should not be transformed by
`CssLinkResourceTransformer`s, since rewriting those would need to
uncompress/transform/recompress. This would lead to poorer performances
than resolving plain resources and delegating compression to the
container.
This commit checks for `GzippedResource` instances in
`CssLinkResourceTransformer` and avoids processing them.
Issue: SPR-14773
cb44f2746e