Support multi-line failure/error messages

### What feature do you want to see added?

In my tests, I sometimes output multiline failure messages. This is useful, for example, when a test is comparing json output.
This doesn't appear to be supported, new lines are converted to spaces.
I am using JUnit and xUnit plugins, but I'm pretty sure this comes from this plugin.

Eg:
```xml

```
becomes:

### Upstream changes

_No response_

### Are you interested in contributing this feature?

_No response_

Start by tracing how the Jenkins JUnit plugin reads and displays failure messages from the XML example, especially the JUnit and xUnit plugin paths mentioned in the report. Reproduce the example with multiline text and verify that the rendered failure preserves line breaks instead of converting them to spaces.

Written by the indexing model from the issue text.