Add support for Mermaid invisible links

[dwelden]

Mermaid diagrams with invisible links result in displaying the markdown text instead of a diagram when attempting to export JPEG. The temporary HTML page that is generated does support the invisible links.

Code example that renders here correctly but fails on Export to JPEG:

%%{ 
    init: {
        'theme': 'base',
        'themeVariables': {
            'lineColor': '#646468',
            'fontFamily': "century gothic"
        }
    }
}%%
    flowchart LR
    classDef Domain fill:#193062,color:#FFF,stroke:#646468
    classDef Subdomain fill:#FAE073,color:#646468,stroke:#646468
    classDef Hub fill:#E9E9E9,color:#646468,stroke:#646468
        d(Domain):::Domain
        s(Subdomain):::Subdomain
        h[(Hub)]:::Hub
        d ~~~ s ~~~ h

Windows 10 VS Code 1.89.0 Markdown PDF 1.5.0 Mermaid Server https://cdn.jsdelivr.net/npm/[email protected]/dist/mermaid.min.js (also fails with https://unpkg.com/browse/[email protected]/dist/mermaid.min.js).