Upgrade to Mermaid 11

What does this MR do and why?

Upgrade to Mermaid 11.

The feature flag is at 100% and is stable. Let's make it official!

I've explicitly chosen to keep some artefacts of the upgrade in the codebase, such as the npm alias, references to "mermaid_v11", and some lists which now only contain 'mermaid_v11' -- we will very likely want to upgrade to Mermaid 12 someday, so let's make it easier for ourselves.

References

• [FF] use_mermaid_v11 -- Use Mermaid 11 instead ... (#596120)
• Update mermaid to version 11.0.0.0+ (#491514 - closed)

How to set up and validate locally

1. Check out the branch; make sure you yarn and probably restart your GDK.
2. Enter a Mermaid 11-only diagram type into a Markdown field, such as:

   ```mermaid
   packet
   title UDP Packet
   +16: "Source Port"
   +16: "Destination Port"
   32-47: "Length"
   48-63: "Checksum"
   64-95: "Data (variable length)"
   ```

3. It should Just Work™.

MR acceptance checklist

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