Improve file locations in the Roslyn Sarif reports for source generator files

Hello,

In the Roslyn Sarif reports the file locations for source generator code are not pointing to the right location on disk, even if EmitCompilerGeneratedFiles is set to true.

In SonarSource we parse these reports in order to import the raised issues and having the full path in the report (similar with the one for non generated code) will help us and the community write better tools which handle these files.

Expected Behavior:

{
  "ruleId": "S1144",
  "level": "warning",
  "message": "Remove the unused private method 'UnusedMethod'.",
  "locations": [
	{
	  "resultFile": {
		"uri": "file:///c:/src/SourceGeneratorPOC\SourceGeneratorPOC\obj\Debug\netcoreapp3.1\generated\SourceGeneratorPOC.Generators\SourceGeneratorPOC.SourceGenerator\Greetings.cs",
		"region": {
		  "startLine": 7,
		  "startColumn": 9,
		  "endLine": 7,
		  "endColumn": 47
		}
	  }
	}
  ],
}

Actual Behavior:

{
  "ruleId": "S1144",
  "level": "warning",
  "message": "Remove the unused private method 'UnusedMethod'.",
  "locations": [
	{
	  "resultFile": {
		"uri": "SourceGeneratorPOC.Generators/SourceGeneratorPOC.SourceGenerator/Greetings.cs",
		"region": {
		  "startLine": 7,
		  "startColumn": 9,
		  "endLine": 7,
		  "endColumn": 47
		}
	  }
	}
  ],
}

Thank you!