implement key to expand all nodes in View Results Tree

**Mathijs Groen** ([Bug 63133](https://bz.apache.org/bugzilla//show_bug.cgi?id=63133&redirect=false)):
Could there key added a function (preferrable to be initiated by a hotkey) to expand/collapse all nodes in the View Results tree Listener?

We have our tests build up in hierarchy (using Include controllers calling testfragments in different folders). This works fine but in the View Results Tree I now need to open all nodes with a mouseclick one-by-one, this is cumbersome.

Would be better if by using a keystroke to expand/collapse all nodes in the View Results Tree at once.

See attached screenshot.

Created attachment [2019-01-30_14-45-46.png](https://apache.github.io/jmeter-bugzilla-attachments/33/63133/36408/2019-01-30_14-45-46.png): illustration

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