Patatrack hackathon4

[rovere]

Please, keep in mind that this PR will bring in most of the work done by Vincenzo for the PV on GPU.
If needed, we could try to factor that part out (but not the global error part)....

[cmsbot]

A new Pull Request was created by @rovere (Marco Rovere) for CMSSW_10_2_X_Patatrack.

It involves the following packages:

DataFormats/GeometrySurface
HeterogeneousCore/CUDAUtilities
RecoLocalTracker/SiPixelClusterizer
RecoLocalTracker/SiPixelRecHits
RecoPixelVertexing/Configuration
RecoPixelVertexing/PixelTrackFitting
RecoPixelVertexing/PixelTriplets
RecoPixelVertexing/PixelVertexFinding
SimTracker/TrackerHitAssociation

The following packages do not have a category, yet:

HeterogeneousCore/CUDAUtilities
Please create a PR for https://github.com/cms-sw/cms-bot/blob/master/categories_map.py to assign category

@cmsbot, @fwyzard can you please review it and eventually sign? Thanks.

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[fwyzard]

@rovere can you rebase this PR on the HEAD of CMSSW_10_2_X_Patatarack ?
The conflicts likely come from having merged the latest PR from @VinInn and the subsequent optimisations.

[fwyzard]

...and provide a more descriptive title and description, as they will become the commit message for the merge :-)