Icon class name(s) for the item (e.g. 'codicon codicon-feedback').
OptionalpriorityPriority among the items. Can be negative. The smaller the number the left-most the item will be placed in the toolbar. It is 0 by default.
OptionaltooltipOptional tooltip for the item.
The command to execute when the item is selected. The handler will receive the
RequestNodeorResponseNodeas first argument.