Add zoom marquee selection to spectral vertical ruler

### Description

In AU3 the User is able to set the upper and lower bounds of their spectral vertical ruler by dragging out a marquee selection in the ruler area.

1. User has vertical scale enabled and track in spectral view (cursor should be crosshair)

2. User clicks and drags and a dashed line appears in the ruler and extends over the entire track

3. User releases their mouse and the vertical scale updates with the upper and lower bounds set to the corresponding edges of the selection.

Start by locating the spectral view's vertical ruler and mouse-drag interaction entry points in the Audacity source, then run the application with a track in spectral view and the vertical scale enabled. Implement the described marquee behavior and manually verify that dragging updates the upper and lower spectral bounds to the selection edges.

Written by the indexing model from the issue text.