This is an extension allowing the VMC package to run a simulation
with multiple different engines at a time. Tracks can be transferred
among engines during a simulation run based on conditions specified by
the user.

Important notes on the extensions:
  1) This extension preserves backward-compatibility in the sense that
     user code relying on the former version of VMC is still running
     with the extended version. Was tested with GEANT3_VMC@v2-6 and
     GEANT4_VMC@v3-6-p1.
  2) A shared simulation is only possible when TGeo is used for geometry
     construction and navigation.
  3) A TMCManager singleton object is responsible for handling multiple
     engines and can be obtained on request calling
     TVirtualMCApplication::RequestManager() during construction of the
     user application class.
  4) The introduced TMCParticleStatus objects hold additional
     information to keep track of properties when a track is transferred
     between engines.
  5) When a track is interrupted in one engine to be transferred to
     another, the geometry state is cached in the form of a
     TGeoBranchArray object. It will be used to initialize the navigator
     when this track is picked up for further transport in the next
     engine. This is especially useful/required when a track is
     transferred at a volume boundary in order to be picked up in the
     entered volume and not in the one just left. This is a main reason
     why geometry management is forced to be done via TGeo.

A more comprehensive introduction concerning the usage and
implementation in the user code can be found in the
montecarlo/vmc/README.md

Further note:
  This commit also applies the clang format to the modified and new
  files.

The getNameAsString interface causes a lot of temporary allocations.
The analysis if a decl is a cling-style wrapper can work only on a
simple declarations on the global scope.

This patch filters out complex declarations (eg in namespaces) and
checks only the identifier content.

The patch reduces the memory footprint difference shown in root-project/root#3012.

This allows TMVA to create a pool of threads on demand and fixes ROOT-10034

This reverts commit 3efc1356.

Duplicating Cling_Runtime and Cling_Runtime_Extra in both module.modulemap
and module.modulemap.build causes redefinition errors if -Dbuiltin_clang=Off.
We should not duplicate the cling runtime modules in both modulemaps.

This is a cherry pick of the loader.py in cppyy-backend
version clingwrapper-1.7.2, which has the new treatment of
CLING_STANDARD_PCH and its setting to 'none' to prevent
the PCH check by Cppyy.

A complete update will come for the three packages of Cppyy
once the functionality of this PR:
https://github.com/root-project/root/pull/3579
is merged into TCling.

Fix number of returned number of entries when adding TH2Poly's. Now SetBinContent change number of entries so the value must be computed before merging

This fixes ROOT-7608.
Move to protected also the functions of TH1 that do not make sense for TH2Poly.
Add a test for getting/setting the bin error

The issue is triggered when using the Python callable converter
of Cppyy.

The fix has been merged already in the CPyCppyy repo:
https://bitbucket.org/wlav/cpycppyy/pull-requests/18

Also, make sure CPyCppyy headers are in the PCH.

This commit contributes to fix the roottest-python-cling tests,
which use TPython, now part of CPyCppyy.

Instead of specifying the location of the PCH, we can just use
the magic word 'none' to tell cppyy not to check the PCH.
In both cases, the objective is to avoid a warning from cppyy
when importing it.

Tested with 6.16/00

When using RooAddPdfs in a convolution, it has to be ensured that the convolution observable remains the reference for interpreting the coefficients of the RooAddPdf. This is because a new binned range has to be constructed to perform discrete FFTs. Interpreting coefficients with respect to this internal range yields coefficients that depend on the properties of this range. This patch disentangles these.

ROOT-9653
ROOT-7183
ROOT-9419