Rename some `MergedAnnotation` methods to prevent using parent/child
terminology, specifically:
`getDepth()` has been renamed `getDistance()`
`getParent()` has been renamed `getMetaSource()`
`getTypeHierarchy()` has been renamed `getMetaTypes()`
The parent child naming was particularly confusing given that the
parent/child relationships were inverted from the way that a lot of
users think about meta-annotations. For example, a `@RequestMapping`
having a parent of `@GetMapping` feels odd given that `@GetMapping`
is the thing declaring the meta-annotation relationship.
The new method names are designed to align more closely with existing
terms. For example, `getMetaSource` hints at the relationship with
`isMetaAnnotated` and `getSource`.
Closes gh-22946
e386e53f92