Prior to this commit, BeanOverrideBeanFactoryPostProcessor replaced
existing bean definitions with "pseudo" bean definitions; however, that
is unnecessary. An existing BeanDefinition is suitable as-is and does
not need to be replaced with a pseudo/fake definition.
To address that, this commit reregisters an existing bean definition
and only registers a new bean definition when creating a bean
definition for a nonexistent bean.
As a side effect, we no longer need to copy primary and fallback flags.
Closes gh-33627
a21c557101