flattenedDiagramName
fun flattenedDiagramName(componentName: String, at: AnalysisType, depth: AnalysisDepth, mode: MergeMode, diagram: DiagramType, summary: SummaryType, slug: String, ext: String): String
Single-segment filename suitable for Dokka's flat images/ dir. Path separators become -- (double dash); folder names are snake_case so single dashes don't appear inside any segment.
Example return: MyComponent--data_and_control_flow_analysis--per_group--all_sinks--data_flow_diagram--summarized--mysink.dot