Add JSONC support for .vscode configuration files

Fixes #269824

• Support settings.jsonc, tasks.jsonc, launch.jsonc, mcp.jsonc, and extensions.jsonc
• Maintain backward compatibility with .json files, taking precedence
• Update configuration loading to try .json first, then .jsonc as a fallback
• Add comprehensive test coverage for JSONC file resolution
• Update split settings editor to handle both .json and .jsonc patterns
• Enhance workspace extension recommendations to support both formats

Manually tested with local instance, it works