Show translations instead of plural key for entries from stringdict files

[PaulTaykalo]

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Currently, SwiftGen, when parsing .stringdict for earch entry generates "translation" in format /// Plural format key: "%#@apples@", which is a bit confusing. Since for other files i.e. .strings, real translation will be included.

So this PR changes what will be returned in the Strings.Entry. Now, real translation will go to the translation, and additional optional parameter formatKey added for the cases, if formatKey needed for the templates (i.e. in comments)

[PaulTaykalo]

I'm currently reading the whole conversation why is plularFormat There, But still, thinkg that from the developer's perpsective - having translation (any translation) in the Entry is more correct than having "format" in the translation key. https://github.com/SwiftGen/SwiftGen/pull/634