Support for Light Theme in Formatter

Currently, the Formatter class in [formatter.ts](vscode-file://vscode-app/usr/share/code/resources/app/out/vs/code/electron-browser/workbench/workbench.html) is designed with a Codeforces-themed dark styling. This issue proposes adding support for a light theme while ensuring the formatter remains flexible for future theme additions.

**Scope**

Modify the **Formatter** class to support a light theme.
Refactor the **Formatter** class to make it extensible for additional themes in the future.
Proposed Changes

**Theme Support:**

Introduce a mechanism to switch between themes (e.g., light and dark).
Define a light theme with appropriate colors and styles.

**NOTE**
Ensure the current dark theme remains the default to avoid breaking existing functionality.

**Acceptance Criteria**

- A light theme is implemented with appropriate colors and styles.
- The Formatter class is refactored to support multiple themes.
- The dark theme remains the default.
- Unit tests are added or updated to cover the new functionality.

**Additional Notes**

This issue focuses solely on modifying the Formatter class. No changes to other parts of the application are required.
Suggestions for design patterns or approaches to make the formatter extensible are welcome.

References

Current implementation: [src/formatter.ts](vscode-file://vscode-app/usr/share/code/resources/app/out/vs/code/electron-browser/workbench/workbench.html)