Update the `isAncestorOf` method of SpringConfigurationPropertySources
so that legacy names are considered for the system environment.
Prior to this commit, binding a property such as `my.camelCase.prop`
would detect `MY_CAMELCASE_PROP` but not `MY_CAMEL_CASE_PROP` in
the system environment.
Fixes gh-14479
Co-authored-by: Phillip Webb <pwebb@pivotal.io>