Fix 404 URLs on path-based i18n projects

[blittle]

WHY are these changes introduced?

Hydrogen offers merchants the ability to easily set up localized paths for new projects. This means the active country and language code are in a path prefix. For example, a product page exists at /fr-ca/products/hydrogen. The locale prefix is optional, so /products/hydrogen also exists, where a default locale is used. The way to configure this in Remix is with optional route segments. Hydrogen generates a route file named: ($locale).products.$productHandle.tsx.

This works well until the user goes to an unknown route. In this case, the app needs to return a 404 response. Each of the following routes need to generate a 404:

1. https://hydrogen.shop/doesNotExist
2. https://hydrogen.shop/doesNotExist/products

The problem is that, even though neither route exists, both routes still match for Remix. This is because ($locale) is an optional segment, and the index route and products route both match and render at each route respectively.

The fix is to add a pathless route ($locale).tsx that includes logic to throw a 404.

WHAT is this pull request doing?

1. Update the demo store and starter template to include a ($locale).tsx pathless route.
2. Add logic to the CLI to make sure it gets generated on new projects.

HOW to test your changes?

Test the following routes:

1. 404 - /doesNotExist
2. 404 - /doesNotExist/collections
3. 404 - /en-ca/doesNotExist
4. 200 - /collections
5. 200 - /en-ca/collections

Test each of these routes on both the demo store and a newly generated starter template. Do not test inside the skeleton template directly (because it doesn't have i18n configured). Instead, generate a new project with h2 init at the root of the repo.

Also verify:

1. ($locale).jsx is generated for JS projects
2. ($locale).tsx is generated for TS projects
3. No ($locale).tsx is generated for non-path-based i18n projects

Post-merge steps

Checklist

• I've read the Contributing Guidelines
• I've considered possible cross-platform impacts (Mac, Linux, Windows)
• I've added a changeset if this PR contains user-facing or noteworthy changes
• I've added tests to cover my changes
• I've added or updated the documentation

[frandiox]

I've updated it a bit to work with adapter option and h2 generate route command 👍