i18n: Use %s placeholders in rest api translation strings

[ramiy]

This patch has several changes:

1. It replaces the register_routes() method with a %s placeholder.
2. It replaces the apostrophe around the %s placeholders with <code> tags.
3. It adds translators comments to all the translation strings.

[ramiy]

The patch also adds a period at the end of the sentence and it has a small text change to match the other string.

Old translation strings:

• The register_routes() method must be overridden
• Method '%s' not implemented. Must be overridden in subclass.

New translation strings:

• Method %s must be overridden.
• Method %s not implemented. Must be overridden in subclass.

[ramiy]

Reference: ​https://translate.wordpress.org/projects/wp/dev/he/default?filters%5Bterm%5D=must+be+overridden&filters%5Buser_login%5D=&filters%5Bstatus%5D=current_or_waiting_or_fuzzy_or_untranslated&filter=Filter&sort%5Bby%5D=priority&sort%5Bhow%5D=desc

[ramiy]

Clarification about the text changes - this patch replace 12 strings:

• Method '%s' not implemented. Must be overridden in subclass.

With:

• Method %s not implemented. Must be overridden in subclass.

---

And also, it replaces one string:

• The register_routes() method must be overridden

With:

• Method %s must be overridden.

[SergeyBiryukov]

I'd suggest only changing the register_routes() string and leaving the Method '%s' not implemented strings as is, I'm not sure HTML is allowed in all contexts there.

[SergeyBiryukov]

In 41587:

I18N: Replace method name in a translatable string in WP_REST_Controller::register_routes() with a placeholder.

Props ramiy.
Fixes #41667.

[ramiy]

In my patch I've also added translators comments to all the other translators strings using %s placeholder. We need this data for GlotPress.

[SergeyBiryukov]

Right, sorry, missed that.

[SergeyBiryukov]

In 41591:

I18N: Add translator comments for placeholders in WP_REST_Controller strings.

Props ramiy.
Fixes #41667.