Auto-create an instrument when drag/drop audio clip onto whitespace

[Brent Core]

When I create a new project with zero instruments, there is no obvious way to drag and drop an audio clip onto the whitespace (in the "Recording" workspace). I have to first create an instrument, then drag and drop the clip on the meter bar. Maybe when a user drops an audio clip into the whitespace, an "Audio File" could be automatically created with the clip at 0 seconds so there is less clicking involved.

[Laszlo Pandy (laszlok)]

This goes along with bug #70354 which aims to make adding an event much more obvious than it currently is.

[Brent Core (brentcore2)]

also, Bug #71018 suggests a clever way to handle the UI for this. For example, suppose Jean-Francois Arseneau's suggestion to darken the shade for unused space is implemented. When an audio clip is dragged onto this unused space, a visual cue can be enacted to show where the auto-generated "Audio Clip" instrument would go. This would occur before the user has released the mouse clip, i.e. the user has "dragged" the clip onto the workspace but not yet "dropped". This visual cue can be the un-darkening of the not-yet-created row with a preview thumbnail of the instrument icon and a visual creation of the meter track. This entire visual cue can also be slightly blurred until the user actually releases the mouse button, thus dropping the clip onto the workspace and auto-creating the instrument.

This serves to make it obvious to the user that a clip can in fact be dragged and dropped onto the workspace.