Add language label to code blocks in read-only modes

[fonty422]

When using a code block in the static or read-only editor, it loses any label indicating the language selected while in edit mode.
Hopefully it's simple to implement, and perhaps can contain an attribute to enable/disable the label (some may not want it)
While I can modify the local downloaded package to do this, it makes it hard to upgrade/update the version.

Unless someone knows of a simple way to add this feature via custom input plugins or similar methods that will survive version changes?

[zbeyens]

Implemented in #4989.

What changed:

• Read-only and static code blocks now render the persisted language label.
• The label can be hidden with showLanguageLabel={false}.

Verified with pnpm check and browser proof on /docs/examples/code-block in Viewing mode.