Implement support for exporting SVG

[tortmayr]

Add a command + key binding to trigger the svg export. Potentially also add it to the vscode counterpart of the "diagram menu" (#201 )

[lforst]

PR eclipse-glsp/glsp-vscode-integration#15 adds the possibility to export a diagram as SVG using a menu contribution. However, a key binding for this functionality has not been added yet.

I would still recommend to consider this issue as resolved, because adding a keybinding for a command is a basic procedure using the VS Code API. All the components necessary to register such key bindings have already been implemented in the PR above.

[tortmayr]

Closing this issue. A follow-up issue for the missing keybinidng has been created