Add taskoutput tool result formatter

[LasmarKhalifa]

Closes #978

Taskoutput's content is a String that resembles XML content, something like:
content: "<status>completed</status><output>Some output</output>"
However it is not proper XML. It contains no shared root and special characters are not escaped.

This implementation uses regex to extact the information we need from the content.

Prototypes [1] [2] [3] explored various options, but regex was ultimately the best suited for our current needs.

[LasmarKhalifa]

• Use tag_text in error_lines #993
• Add taskoutput tool result formatter #992 👈 (View in Graphite)
• main

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[dersam]

Merge activity

• Jun 26, 5:23 PM UTC: A user started a stack merge that includes this pull request via Graphite.
• Jun 26, 5:24 PM UTC: Graphite rebased this pull request as part of a merge.
• Jun 26, 5:24 PM UTC: @dersam merged this pull request with Graphite.