Port the whole pixel workflow to new heterogeneous framework

[fwyzard]

• port the whole pixel workflow to new heterogeneous framework
• implement a legacy cluster to SoA converter for the pixel RecHits
• update the vertex producer to run on CPU as well as GPU

Note: the customisation functions have been renamed, and must now be called after the conversion to unscheduled:

...
# end of customisation functions
# do not add changes to your config after this point (unless you know what you are doing)
from FWCore.ParameterSet.Utilities import convertToUnscheduled
process = convertToUnscheduled(process)

# run the pixel reconstruction on GPU
from RecoPixelVertexing.Configuration.customizePixelTracksForProfiling import customizePixelTracksForProfilingGPUOnly
process = customizePixelTracksForProfilingGPUOnly(process)

# run the pixel reconstruction on GPU, and copy the SoA's to the CPU
from RecoPixelVertexing.Configuration.customizePixelTracksForProfiling import customizePixelTracksForProfilingEnableConversion
process = customizePixelTracksForProfilingEnableTransfer(process)

# run the pixel reconstruction on GPU, copy the SoA's to the CPU, and convert to the legacy format
from RecoPixelVertexing.Configuration.customizePixelTracksForProfiling import customizePixelTracksForProfilingEnableTransfer
process = customizePixelTracksForProfilingEnableConversion(process)