Fix incorrect namespacing of `Resolvers::ValidateCodeownerFileResolver`
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Currently the `Resolvers::ValidateCodeownerFileResolver` is incorrectly namespaced in the `EE` namespace. This namespace is reserved for CE extensions but this resolver is an EE only class not a CE extension.
While we're moving this we should also fix the naming. It should either be ValidateCodeowner**s**FileResolver or ValidateCode**O**wnersFileResolver.
Either way makes sense IMO. We're either validating the `CODEOWNERS` file or the file for the `Code Owners` feature. As we can't uppercase the whole word I'd personally lean towards `ValidateCodeOwnersFileResolver`
The main thing here is the namespacing so wouldn't worry to much about the naming.
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