Upgrade Mermaid to 11.13.0

What does this MR do and why?

It's a brand new day. Let's try Mermaid 11.13.0, which comes with https://github.com/mermaid-js/mermaid/pull/7276 merged.

References

• Upstream Mermaid 11 has backwards compatibility... (#554889) outlines some issues that have been holding us back from the Mermaid 11 upgrade. It seems that, as of now, all four problems main problems outlined have been addressed.
• Update mermaid to version 11.0.0.0+ (#491514) is an earlier request to upgrade.
• Update mermaid to 11.4.1 (!171452 - closed) is an earlier attempt which ran aground.

Screenshots or screen recordings

Before	After

Before, an unsupported diagram (example given in !171452 (closed)'s description under "How to set up and validate locally") doesn't render, while a supported one does. After, both render correctly.

How to set up and validate locally

1. Check out the branch, yarn to install the latest dependencies.
2. If your GDK is a feisty one, you may wish to restart it.
3. Ensure you haven't enabled Mermaid-via-Kroki from /admin/application_settings/general#js-kroki-settings ("Mermaid" should be unticked).
4. Try creating Mermaid graphs with ```mermaid syntax. Existing ones should continue to work well.

The the three diagrams below (first from !171452 (closed), two more concocted from various sources) exercise all four of the issues mentioned at #554889:

```mermaid
%%{init: { "fontFamily": "GitLab Sans" }}%%
flowchart RL
accTitle: Subgroup membership
accDescr: How users become members of a subgroup - through direct, indirect, or inherited membership.

  subgraph Group A
    A(Direct member)
    B{{Shared member}}
    subgraph Subgroup A
      H(1. Direct member)
      C{{2. Inherited member}}
      D{{Inherited member}}
      E{{3. Shared member}}
    end
    A-->|Direct membership of Group A\nInherited membership of Subgroup A|C
  end
  subgraph Group C
    G(Direct member)
  end
  subgraph Group B
    F(Direct member)
  end
  F-->|Group B\nshared with\nGroup A|B
  B-->|Inherited membership of Subgroup A|D
  G-->|Group C shared with Subgroup A|E
```

```mermaid
flowchart TD
A[GitLab frontend] -->B["`AiAction **GraphQL** mutation`"]
B --> C[2. Llm::ExecuteMethodService]
C --> D[Hmm, `ok`.]
```

```mermaid
sequenceDiagram
    Alice ->> Bob: Hello Bob, how are you?
    Bob-->>Jo=hn: How about you Joh=n?
    Bob--x Alice: I am good thanks!
    Bob-x Jo=hn: I am good thanks!
    Note right of Jo=hn: Bob thinks a long<br/>long time, so lo=ng<br/>that the text does<br/>not fit on a row.

    Bob-->Alice: Checking with Jo=hn...
    Alice->Jo=hn: Yes... Jo=hn, how are you?
```

No errors, no \ns.

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