Migrate all `code` and `codenew` shortcodes to `code_sample`

While working on another issue (#56569), I found out that we currently have 3 identical shortcodes: `code`, `codenew`, and `code_sample`. Here's the issue revealing its story (#42203), but briefly: we had `codenew` and wanted to rename it to `code`, but during this migration decided to stick with `code_sample` because it's easier (than simple `code`) to find with `grep` and alike. Today, we have:
- `code` used across _two_ English pages (and _one_ `zh-cn` page);
- `codenew` used across _zero_ English pages (and a few pages, but across _numerous_ localisations);
- `code_sample` used everywhere else.

Since the first two shortcodes are barely in use, I suggest facilitating our migration to `code_sample`, hopefully resulting in the complete removal of [outdated] `/shortcodes/code.html` and `/shortcodes/codenew.html` files. Currently:
- `code.html` and `codenew.html` are completely identical;
- `code_sample.html` is a more advanced version of them, but still compatible (so there would be a simple replacement of `{{% code[new] ...` to `{{% code_sample ...`).

If that sounds reasonable, I'm ready to prepare all relevant PRs across all the localisations involved.

Start by searching the English and localized content for `code` and `codenew` shortcode uses, then inspect `/shortcodes/code.html`, `/shortcodes/codenew.html`, and `/shortcodes/code_sample.html` to confirm compatibility. Replace the remaining uses with `code_sample` across the affected localisations and remove the two outdated shortcode files. Done means no relevant `code` or `codenew` uses remain and the migration covers the listed language pages.

Written by the indexing model from the issue text.