Rename theme-app-extension-next to theme-app-extension

[jamesmengo]

WHY are these changes introduced?

Follow up on - https://github.com/Shopify/cli/pull/4592

Renames a file that was deleted in the previous PR (replacing theme-app-extension with theme-app-extension-next)

I split this into a different PR to avoid polluting the diff of this change

[github-actions[bot]]

Thanks for your contribution!

Depending on what you are working on, you may want to request a review from a Shopify team:

• Themes: @shopify/advanced-edits
• UI extensions: @shopify/ui-extensions-cli
  • Checkout UI extensions: @shopify/checkout-ui-extensions-api-stewardship
• Hydrogen: @shopify/hydrogen
• Other: @shopify/app-inner-loop

[github-actions[bot]]

Coverage report

St.:grey_question:	Category	Percentage	Covered / Total
🟡	Statements	72.81%	8552/11746
🟡	Branches	69.77%	4200/6020
🟡	Functions	71.81%	2209/3076
🟡	Lines	73.14%	8095/11068

Show new covered files 🐣

St.:grey_question:	File	Statements	Branches	Functions	Lines
🟢	... / theme-app-extension.ts	93.75%	90%	83.33%	93.55%

Test suite run success

1947 tests passing in 876 suites.

Report generated by 🧪jest coverage report action from d7671f995819cca155bd52cf739e84a025c444f1

[github-actions[bot]]

We detected some changes at either packages/*/src or packages/cli-kit/assets/cli-ruby/** and there are no updates in the .changeset. If the changes are user-facing, run "pnpm changeset add" to track your changes and include them in the next release CHANGELOG.