Add Export to Mermaid/DrawIO to bicep visualizer export process

Shenglong Li demoed the new Bicep Visualizer functionality in the March community call on 4/1.

Currently, the only supported export format is PNG.

Adding Mermaid and DrawIO export would be extremely useful for further refining diagrams for documentation, such as adding grouping boxes and labels. This would also be extremely useful for Diagram as Code functionality and checking in documentation into source control.

Start by locating the Bicep Visualizer export process and the existing PNG export path. Determine how the visualizer represents diagrams for export, then define Mermaid and DrawIO outputs that preserve the useful diagram structure. Done means both formats can be exported alongside PNG and support documentation and source-control workflows.

Written by the indexing model from the issue text.