create diagramVersionMigrator script

[Yokozuna59]

Currently, some diagram have -v2 prefix, i.e., flowchart-v2 and stateDiagram-v2, indicating there's slightly changes in grammar or/and layout. Most users mayn't be aware of changes required (or need a lot of work) to migrate to the newest version. So by creating this script, it would allow users to have up-to-date code for their diagrams.

We could also add this functionality to https://mermaid.live, add something like a button that updates the code.

Note: I'm not sure if we should make this part of mermaid-live-editor or mermaid, but I feel like adding it to mermaid and provide an API for it would be a better choice.

[Yokozuna59]

We also have handle the new keywords when they're applied (see #4542).