Math in mermaid diagrams does not render

[AllexVeldman]

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Mermaid supports math expressions in some diagrams.

Related Issue in the mermaid repo: mermaid-js/mermaid#5482

These expressions are not shown as part of Github Issues, below are the examples from the documentation:

```mermaid
graph LR
      A["$$x^2$$"] -->|"$$\sqrt{x+3}$$"| B("$$\frac{1}{2}$$")
      A -->|"$$\overbrace{a+b+c}^{\text{note}}$$"| C("$$\pi r^2$$")
      B --> D("$$x = \begin{cases} a &\text{if } b \\ c &\text{if } d \end{cases}$$")
      C --> E("$$x(t)=c_1\begin{bmatrix}-\cos{t}+\sin{t}\\ 2\cos{t} \end{bmatrix}e^{2t}$$")
```

graph LR
      A["$$x^2$$"] -->|"$$\sqrt{x+3}$$"| B("$$\frac{1}{2}$$")
      A -->|"$$\overbrace{a+b+c}^{\text{note}}$$"| C("$$\pi r^2$$")
      B --> D("$$x = \begin{cases} a &\text{if } b \\ c &\text{if } d \end{cases}$$")
      C --> E("$$x(t)=c_1\begin{bmatrix}-\cos{t}+\sin{t}\\ 2\cos{t} \end{bmatrix}e^{2t}$$")

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```mermaid
sequenceDiagram
    autonumber
    participant 1 as $$\alpha$$
    participant 2 as $$\beta$$
    1->>2: Solve: $$\sqrt{2+2}$$
    2-->>1: Answer: $$2$$
    Note right of 2: $$\sqrt{2+2}=\sqrt{4}=2$$
```

sequenceDiagram
    autonumber
    participant 1 as $$\alpha$$
    participant 2 as $$\beta$$
    1->>2: Solve: $$\sqrt{2+2}$$
    2-->>1: Answer: $$2$$
    Note right of 2: $$\sqrt{2+2}=\sqrt{4}=2$$

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This is indicated as added since v10.9.0 while Github is at:

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