Made L10n.tr not use bare strings as formats.

[grigorye]

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This addresses #1039, by introducing a specialized variant of tr for argument-less calls used with wrappers generated for bare strings. Beware that this is a breaking change for the cases where %% had to be used before in bare strings.

[djbe]

I should add this to some sort of frequently asked questions. Do a search through the issues/PRs, and you'll find multiple discussions about this.

The big problem with not formatting strings for those with no parameters, is that it creates a double standard for encoding percentages:

• For strings with parameters, if you to "print" the string 100%, you'll need to provide the string 100%%.
• For strings without parameters, you'll need to provided the string 100%.

We do not want our users to have to deal with these inconsistencies. There's unfortunately no good solution for this 🤷 What we usually recommend is providing your own lookupFunction (see the docs), and do a check for no/some parameters. Or a custom template.