Add missing deprecated errors methods

[BrianHawley]

Fixes for Rails/DeprecatedActiveModelErrorsMethods:

• The values, to_h, and to_xml methods are deprecated too.

---

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• The PR relates to only one subject with a clear title and description in grammatically correct, complete sentences.
• Wrote good commit messages.
• Commit message starts with [Fix #issue-number] (if the related issue exists).
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• Squashed related commits together.
• Added tests.
• Ran bundle exec rake default. It executes all tests and runs RuboCop on its own code.
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• If this is a new cop, consider making a corresponding update to the Rails Style Guide.

[BrianHawley]

There's no check for errors.each do |key, value| because I don't know how to specify that. The each method is only deprecated if you pass a block with two parameters to it; the new each method takes a block with one parameter. This isn't easily autocorrectable, but the manual change could be given as an example in docs.

[BrianHawley]

@koic as requested.

[BrianHawley]

@koic rebased.

[koic]

There's no check for errors.each do |key, value| because I don't know how to specify that. The each method is only deprecated if you pass a block with two parameters to it; the new each method takes a block with one parameter. This isn't easily autocorrectable, but the manual change could be given as an example in docs.

Yep. I think it can be solved separately from this PR. Can you rebase with the latest master branch?

[BrianHawley]

@koic rebased.

[koic]

Thanks!