language-tools: VSCode plugin: Syntax highlighting not correctly applied to embedded svelte component in markdown

Describe the bug Syntax highlighting not correctly applied to embedded svelte component in markdown when using “Svelte for VSCode”

To Reproduce Steps to reproduce the behavior:

Put the following inside a markdown document:

```svelte
<script>
  import { onMount } from "svelte";

  export let data = undefined;
  let dom_node;

  onMount(() => {
    Plotly.newPlot(dom_node, data, {barmode: 'stack'});
  });
</script>

<div id="plotDiv" bind:this={dom_node}></div>
```

For example a code snippet that is treated in a way you don’t expect.

Expected behavior

Expected similar syntax highlighting to what I see when viewing a svelte file with that content.

Actual behaviour

Get somewhat incorrect / inconsistent formatting (see screenshots)

Screenshots If applicable, add screenshots to help explain your problem.

View for a svelte component (correct):

View for a svelte component embedded in markdown (incorrect):

System (please complete the following information):

• OS: Mac and Windows 10
• IDE: VSCode
• Plugin/Package: “Svelte for VSCode”

Additional context Add any other context about the problem here.