video: Don't change the `VideoOverlayComposition` constructor API based on feature flags
requested to merge slomo/gstreamer-rs:videooverlaycomposition-no-api-changes-with-features into main
Feature flags are additive and a higher feature might be enabled by some other dependency, which then can cause code that assumes the other API fail to compile.
Still implement the constructor separately per version to make it clear to the compiler that the constructor can't fail at all in newer versions.