Theme support for JSON formatter (e.g. Dracula theme)

[DEVigodE]

Currently, the JSON formatter extension uses a single fixed visual style.
This issue proposes adding theme support, allowing users to choose between different visual themes (e.g. Dracula, Light, Dark) to improve readability, accessibility, and user comfort.

The theme system should be extensible by design, so new themes can be added without touching the core formatting logic.

1. 🎯 Goals

• Allow users to select a visual theme
• Support well-known themes (e.g. Dracula)
• Improve readability for long and complex JSON files
• Make the theme system scalable and maintainable

2. 🧩 Functional Requirements

• Theme selector (dropdown or similar UI control)
• Apply the selected theme in real time
• Persist the selected theme between browser sessions
• Define a default theme (e.g. Dracula or Light)

3. 🎨 Theming Scope

• Each theme should define colors for:
• Background
• Default text
• JSON keys
• Strings
• Numbers
• Booleans
• null values
• (Optional) Collapsed / expanded nodes// #