Default to `unknown` signature for GlimmerComponent
Default to `unknown` signature for GlimmerComponent

Co-authored-by: James C. Davis <e61c02d5b2f8a2c28604445e52f5c192743ea1ef@gmail.com>
glimmerjs/glimmer.js,glimmerjs/glimmer.js,glimmerjs/glimmer.js,glimmerjs/glimmer.js