[compiler] Clone computation block in change detection mode

Summary: In change-detection mode, we previously were spreading the contents of the computation block into the result twice. Other babel passes that cause in-place mutations of the AST would then be causing action at a distance and breaking the overall transform result. This pr creates clones of the nodes instead, so that mutations aren't reflected in both places where the block is used.

ghstack-source-id: b78def8d8d1b8f9978df0a231f64fdeda786a3a3
Pull Request resolved: https://github.com/facebook/react/pull/30148