feat: replace translate boilerplate with extension in editor

[aonnikov]

No description provided.

[huly-github-staging]

Connected to Huly®: UBERF-13898

[Copilot]

Pull Request Overview

This PR replaces the manual translation boilerplate for editor placeholders with a new I18nPlaceholderExtension that automatically handles internationalization. The extension manages placeholder translations reactively, subscribing to theme store changes for language updates.

• Removed manual translation logic from editor components
• Created a new I18nPlaceholderExtension that extends the TipTap Placeholder extension
• Updated editor kit to use the new internationalized placeholder extension

Reviewed Changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 3 comments.

File	Description
plugins/text-editor-resources/src/kits/editor-kit.ts	Replaced Placeholder import with I18nPlaceholderExtension and updated the kit configuration
plugins/text-editor-resources/src/components/extension/i18nPlaceholder.ts	New extension that handles automatic translation of placeholders with theme store subscription
plugins/text-editor-resources/src/components/TextEditor.svelte	Removed manual translation logic and updated to use new extension options
plugins/text-editor-resources/src/components/CollaborativeTextEditor.svelte	Removed manual translation logic, cleaned up unused imports, and updated placeholder configuration

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