VrtSecInclusive: Migrate developments from 21.2 to master

This MR updates the VrtSecInclusive package to reflect recent developments in 21.2. The core functionality of the package has been tested using the JOs included in share/Vertexing_jobOptions.py. Several classes which have been added to 21.2 are not (yet) included in this MR. These include classes which are either not directly used by the main VrtSecInclusive algorithm:

• SoftBtagTrackSelector
• TrackRandomizer
• IPAugmentor

as well as the updated implementation which already exists in `master':

• MultiSecVertexTool
• AllBVertexAlg

All other updates to 21.2 should be accounted for in this MR. I am leaving this a WIP for now to discuss with experts about whether these other classes should be added and for other core developers to take a look before review.

Tagging @hoide, @kostyuk, @emily, @dtrischu, @cohm