[SAOC 2025] Improving D error messages Weekly Update #4

[Iskaban10]

## [SAOC 2025] Improving D Error Messages Weekly Update #4

## Development of ErrorSinkJSON
- Modified the new error sink class ErrorSinkJSON derived from 
ErrorSink.
- Designed to output compiler diagnostics (errors, warnings, 
deprecations) in JSON format.
- Created printJSONObject() method to print diagnostic in JSON 
format directly to stdout.
- Work under progress for the unittests for errorsinkjson.d

## Challenges Encountered
- Resolving @safe vs @system issues when using vfprintf/vsnprintf.
- Handling null filenames safely in JSON output.
- Ensuring proper import paths to resolve dmd.errorsink without 
creating cycles.

Work in : [https://github.com/Iskaban10/dmd/tree/lsp](URL)