json: add fixed, fixable

[bendrucker]

Extends the JSON formatter to include information about whether issues are fixable or have been fixed, addressing the feature request in #2354.

Changes

• fixable: Set to true when an issue can be automatically fixed
• fixed: Set to true when an issue is fixable AND the --fix flag is used
• Test Updates: Updated all JSON test expectation files to include the new fields

Testing

• Unit tests for different fixable/fixed combinations
• Integration tests for autofix scenarios
• Manual verification with the example from the issue

Example Output

Before

{
  "issues": [{
    "rule": {"name": "terraform_comment_syntax", "severity": "warning"},
    "message": "Single line comments should begin with #",
    "range": {...},
    "callers": []
  }]
}

After

{
  "issues": [{
    "rule": {"name": "terraform_comment_syntax", "severity": "warning"}, 
    "message": "Single line comments should begin with #",
    "range": {...},
    "callers": [],
    "fixable": true,
    "fixed": false
  }]
}

With --fix:

{
  "issues": [{
    "rule": {"name": "terraform_comment_syntax", "severity": "warning"},
    "message": "Single line comments should begin with #", 
    "range": {...},
    "callers": [],
    "fixable": true,
    "fixed": true
  }]
}

Closes #2354

[wata727]

👍