GREL function for {{Creator:Peter Paul Rubens}} {{Institution:Rijksmuseum}} style templates

Wikimedia Commons Wikitext also often contains templates that are formed as {{Creator:Peter Paul Rubens}} or {{Institution:Rijksmuseum}} (note the : instead of a | character). Because such templates are very prevalent (the {{Creator}} and {{Institution}} one are used on millions of files) it would be great to be able to have a dedicated GREL syntax/function for these. See https://commons.wikimedia.org/wiki/Template:Creator and https://commons.wikimedia.org/wiki/Template:Institution for a bit more info about both templates.

In the {{Creator:Peter Paul Rubens}} and {{Institution:Rijksmuseum}} examples respectively, the OpenRefine end user will want to extract Peter Paul Rubens and Rijksmuseum.

This file has both templates, as just one example.