[UI/UX] Workspace for UI Toolkit compatibility

[connffuused]

Is your feature request related to a problem? Please describe.
버전별 UI Toolkit USS 대응을 위한 워크스페이스 구현

Describe the solution you'd like
자체 확장자의 포맷으로 작업하되, Stylesheet Importer를 재사용하여 부분적으로 파싱할 수 있도록 프로세서 구현

Describe alternatives you've considered
A clear and concise description of any alternative solutions or features you've considered.

Additional context
Add any other context or screenshots about the feature request here.