i18n: Use %s placeholders in wp-admin/includes/template.php

[ramiy]

This patch replaces the path, the functions and the actions with %s placeholder. This way translators can't mistakenly changes to wrong function names.

Old translation string:

• Likely direct inclusion of wp-admin/includes/template.php in order to use add_meta_box(). This is very wrong. Hook the add_meta_box() call into the add_meta_boxes action instead.

New translation string:

• Likely direct inclusion of %1$s in order to use %2$s. This is very wrong. Hook the %2$s call into the %3$s action instead.

The patch also adds translators comments and <code> tags around the function/action names.

[SergeyBiryukov]

In 41906:

I18N: Replace hardcoded file name in a translatable string in convert_to_screen() with a placeholder.

Props ramiy.
Fixes #41668.