Spring Apply instanceof pattern matching in RootBeanDefinition

This pull request applies the instanceof pattern matching in the RootBeanDefinition class. This enhancement will improve code readability.

Comment From: sbrannen

Hi @FelixDes,

In the future, please do your best to collect multiple related changes in a PR, since we generally do not like to merge PRs that effectively change a single line of code for style-related reasons.

Comment From: sbrannen

This has been merged into main.

Thanks

Comment From: FelixDes

Thanks a lot for your advice. I'm very glad to see that my PR has been accepted.