Revealjs transformation should move `data-` attributes along with `class`es

Bug description

See https://github.com/posit-dev/shinylive/pull/61

A brief overview: Suppose you have this qmd document:

---
title: "Shinylive RevealJS"
format: revealjs
filters:
  - shinylive
---

## Shinylive R

```{shinylive-r}
#| standalone: true
#| viewerHeight: 420
ui <- fluidPage(
  sliderInput("obs", "Number of observations:",
    min = 0, max = 1000, value = 500
  ),
  plotOutput("distPlot")
)

server <- function(input, output) {
  output$distPlot <- renderPlot({
    hist(rnorm(input$obs))
  })
}

shinyApp(ui, server)
```

This is the HTML structure that shows up normally when rendering the qmd to HTML with format: revealjs commented out:

<pre class="shinylive-r" data-engine="r"><code>#\| standalone: true
...

Shinylive searches for elements with class="shinylive-r", and then looks at the data-engine attribute on that element.

However, when format: revealjs is used, it turns into this:

<div class="sourceCode" id="cb2" data-engine="r">
  <pre class="sourceCode numberSource shinylive-r number-lines code-with-copy">
  <code class="sourceCode">
  <span id="cb2-1"><a href="#cb2-1"></a>#\| standalone: true</span>
  ...

Note that the data-engine attribute is no longer in the same element as class="shinylive-r".

I am guessing this happens because a filter replaces the original <pre> node with a <div>, then creates a new <pre> as a child and and copies the original's class attribute to the new child. I think that the data- attributes should be copied over as well.

Steps to reproduce

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Expected behavior

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Actual behavior

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Your environment

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Quarto check output

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