Support keyboard shortcuts on the non-native sidebar context menu

[solstice-r]

Description

In the tab strip, when you right-click a tab, you can invoke an option by hitting the underlined key in the button's label. This results in being able to duplicate a tab extremely quickly, with just rclick+d which I use often. Sidebery has a duplicate option in its context menu, but lacks the keyboard events to allow me to just hit the "d" key to invoke the button.
There is an option to set this to a shortcut involving the middle mouse button, but I still think it'd be a good idea for accessibility to support this use case.