BUG #14135. Add ability to freeze Python.

When Python support is enabled, on Unix machines, a new option named
PARAVIEW_FREEZE_PYTHON is available. When ON, ParaView will freeze python
modules into the executable. This currently doesn't support matplotlib or numpy.

vtkUtilitiesPythonInitializer module runs vtkFreezePython.cmake to freeze the
python modules and includes the initialization logic in vtkPVPythonInitializer
initialization calls itself.

Change-Id: I5e299374746a872eb9ff3f89beeb5ed2227d6f58
Minimize file opens/stats.

- Set PYTHONHOME to avoid Python from trying to setup a good sys.path.
- Set LC_CTYPE to avoid Python from looking for locale information from system
  configuration.
- Call vtkPVInitializePythonModules() before initializing Python to ensure that
  the environment for frozen Python is initialized correctly before initializing
  Python.

Change-Id: I97ad4398f69878b73078e7411ceaaa8db9e88385
BUG #14147. Improve process initialization times.

- In static builds, we don't need to locate plugins. That is now avoided. This
  saves on several unnecessary filesystem accesses which should improve startup
  time on HPC systems.
- Also avoiding setup of sys.path to find ParaView modules when
  PARAVIEW_FREEZE_PYTHON is true. Since ParaView modules will be frozen, we
  don't need to find site-packages. This avoids further more filesystem
  accesses.

Change-Id: Ib208d5c2308f60b5ecead9bc63ad2a95315788c1
Merge topic 'freeze_python' into next

5959549 BUG #14147. Improve process initialization times.
1246717 Minimize file opens/stats.
bcfa3e6 BUG #14135. Add ability to freeze Python.