Toolbars are not usable while typing parameter values in the VisualEditor template editor. Everything must be typed by hand. This is a regression in comparison to the source editor, where toolbar actions like linking, nowiki, bold, italic, etc. are accessible (many wikis also have additional gadgets there). In VE it's only plain text.
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Description
Event Timeline
Comment Actions
I guess it is relevant only for some parameters based on the type in the templatedata, probably "content" and unspecified parameter type (and maybe "line"?).