Fix disappearing span tags inside code blocks

[ege0zcan]

Problem

The issue was reported in: aws/aws-toolkit-vscode#5732

When there is a closing span tag inside a code block or inline code, it currently disappears and is not rendered. This is caused by old code in mynah-ui that would do some pre-processing on the html contents and replace certain span elements before they were rendered. This causes any span tag to be replaced and removed before they are rendered and this leads to the bug described above

See for example how the following input is rendered currently:

```
<span> span inside a codeblock </span>
```

`<span> span inside inline code </span>`

Solution

To remove the old keepHighlights functionality.

See an example card body that correctly renders the span tags after the fix:

And the test case from above with prompt input containing spans:

Tests

• I have tested this change on VSCode
• I have tested this change on JetBrains

License

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

[Jurredr]

Small issue spotted in follow ups, @dogusata is on it.

[Jurredr]

All fixed!