Support attachments via stdout in the JUnit XML reader

There is a convention for attaching files to the JUnit XML report via the standard output. The file path is embedded in the `[[ATTACHMENT|]]` format:

```xml

```

The convention is supported by many CI systems ([Jenkins](https://plugins.jenkins.io/junit-attachments/), [Azure](https://devblogs.microsoft.com/devops/junit-attachments-support-for-publish-test-results/), etc).

We should support it as well.

Locate the JUnit XML reader and trace how each testcase's system-out content is parsed. Done means recognizing [[ATTACHMENT|]] entries and handling both paths relative to the JUnit XML file and absolute paths, based on the examples in the issue.

Written by the indexing model from the issue text.