Avoid ref overhead when not needed

[ixf]

This reduces RSD's memory overhead in React Native. Measured with https://github.com/ixf/rsd-bench - in this bench it drops retained memory and render times by a couple percent (~5%)

• useStrictDOMElement doesn't need to create a callback ref if no ref was passed to the component
• replace useCallback + useElementCallback (useCallback + useRef) with one useMemo
• reuse default props for images when no aspect ratio needs to be added