feature(PHP): include the current value with enum failure

[dkarlovi]

Purpose is simple: if the property is an enum and the value in the response doesn't match the enum, print the received value in the exception, allowing spec designers to easily fix the spec.

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@jebentier (2017/07), @dkarlovi (2017/07), @mandrean (2017/08), @jfastnacht (2017/09), @ackintosh (2017/09) heart, @ybelenko (2018/07), @renepardon (2018/12)

[wing328]

LGTM