Blender Git Loki

VSE: Support drag and drop for datablocks

For using the Outliner and/or the Asset Browser as scene independent
tools to organize a/v source material is necessary for the users to be
able to drag and drop data blocks into the VSE. This was also an
unfulfilled design target for the Outliner Gsoc project.

Datablocks won't be used directly. Path to file will be passed to strip
add operator instead.

Reviewed By: ISS

Differential Revision: https://developer.blender.org/D13304