[Feature] Add l10n support to CheckoutUiExtension

[ginmrt]

WHY are these changes introduced?

Fixes internal issue

WHAT is this pull request doing?

As part of the Localized Checkout Ui Extensions project, we must update the shopify-cli codebase to allow developers to submit localization files along with their code updates when the Shopify CLI shopify extension push command is executed.

This change applies to the Checkout Extension type of extensions only, for now.

Screenshots

Valid submission

This will be what is shown in the CLI when we will have merged in the code in the Shopify backend that will support this new localization feature.

Valid submission with unrecognized key warning

This will be what is shown in the CLI before and until we will have merged in the code in the Shopify backend that will support this new localization feature.

Note that attempting to publish an extension with this data pushed in before support has been added will fail.

Invalid submission: Invalid locale code

This error appears if the locale code of a given file name is invalid.

Invalid submission: Invalid file extension

This error appears if a file under the /locales folder has an extension type other than .json

Invalid submission: File too large

This error appears if a localization file is larger than the declared limit

Invalid submission: File empty

This error appears if a localization file is completely empty

Invalid submission: Sum of all file sizes too large

This error appears if the combined total size of all localization files exceeds the declared limit

Invalid submission: No default / too many defaults

This error appears if none of the provided locale files are declared as the default locale, or if more than one of them are.

How to test your changes?

• Follow this procedure completely to have a backend to execute the CLI push command against as well as a CheckoutUiExtension extension project setup.
• Create a locales directory at the root of the created extension project of type Checkout Extension
• Create .json files with a valid locale code as the basename. Ensure one of them is suffixed by .default, e.g. en.default.json and fr.json
• Execute the shopify extension push command.

Various simple validations exist, which can be tested by playing around with the filenames under locales and their content. Refer to the screenshots provided above.

Update checklist

• I've added a CHANGELOG entry for this PR (if the change is public-facing)
• I've considered possible cross-platform impacts (Mac, Linux, Windows).
• I've left the version number as is (we'll handle incrementing this when releasing).
• I've included any post-release steps in the section above.

[kumar303]

Nice work, @ginmrt ✨

[ecbrodie]

Left some early feedback. Looks fine overall. I still need to tophat.

[ecbrodie]

@ginmrt do you mind rebasing this PR onto latest main please? This is necessary for being able to support the Spin rewrite. Thank you.

[ecbrodie]

I 🎩'd with a handpicked list of test scenarios and they all checked out for me. Great work Martin.

There is one additional fix that I am requesting before merge though. Once that is addressed, then I can approve.

[ecbrodie]

I still have open feedback that should be given consideration. But overall, I've seen enough from this PR to approve.

[ginmrt]

Ping @jesalerno84 @gonzaloriestra

[gonzaloriestra]

I've added a few suggestions, but the only important one would be to extract the error messages. Otherwise, the code and tests look great (I haven't tested it, as it was done before) 👌

[gonzaloriestra]

Thanks for the changes! It looks great 👍