Unexecuted code block in code blocks should respected the number to braces like inlines

[cderv]

We document this here:
https://quarto.org/docs/computations/execution-options.html#unexecuted-blocks

but the example does not show the {{ python }} as it should

Example:

---
title: "Example"
format: 
   html: default
---

```` markdown
---
title: "A julia engine notebook"
engine: julia
---

```{{{julia}}}
1 + 2
```
````

```{{{julia}}}
1 + 2
```

Results in

Inside the code block, only two braces {{ }} should be removed like for inlines.

it is a regression as it works in 1.3 but not in 1.4

Results with 1.3.450

[cderv]

It comes from dae6fbe where a fix about escaping messed up with this other kind of escaping

• Fixes escaping bugs #8391
• Unescaping new inline code cells inside code blocks is not working correctly. #8389

So we need a solution that correctly works for inline in code block, and code block in code blocks

[cscheid]

This is both a dumb bug and a really hard one to fix. Consider this:

``````
This here is an inline code element:

````{{julia}} code with a three backticks inside it ``` ````

But how should we detect it?
``````

EDIT: I think I found an acceptable way to check for this stuff.