Be able to control Flags from wrapped languages

[Mizux]

Following #2201, the next step could be:

• Python support:
  • Be able to control flags from Python
• Java support:
  • Be able to control flags from Java
• .Net support:
  • Be able to control flags from .Net

EDIT: move LogHandler support in #2489

note: I move these items from #2201, since it's an other optional step.
note: Protobuf custom logging provides LogHandler and can be used as a good starting point
ref: https://github.com/protocolbuffers/protobuf/blob/master/src/google/protobuf/stubs/logging.h

[Mizux]

in Python we now have:

or-tools/examples/python/integer_programming.py

Line 16 in 8c86a97

from ortools.init import pywrapinit

or-tools/examples/python/integer_programming.py

Lines 119 to 123 in 8c86a97

	pywrapinit.CppBridge.InitLogging('integer_programming.py')
	cpp_flags = pywrapinit.CppFlags()
	cpp_flags.logtostderr = True
	cpp_flags.log_prefix = False
	pywrapinit.CppBridge.SetFlags(cpp_flags)

[Mizux]

In .Net:

or-tools/examples/dotnet/csintegerprogramming.cs

Line 15 in 8c86a97

using Google.OrTools.Init;

or-tools/examples/dotnet/csintegerprogramming.cs

Lines 104 to 108 in 8c86a97

	CppBridge.InitLogging("csintegerprogramming.cs");
	CppFlags flags = new CppFlags();
	flags.logtostderr = true;
	flags.log_prefix = false;
	CppBridge.SetFlags(flags);