Modify or-tools code & Add to CMake build

* Remove absl flags -- hardcode values instead
* Cleanup dangling includes
* Remove stats macros
* Replace DCHECK macros with assert statements
* Convert logging macros to the nearest journal equivalent
* Remove dependencies on abseil-cpp
* Manually expand utility macros
* Remove extra semicolons after macro invocations
* Remove protobuf serialization methods
* Replace `MathUtil::Abs` with `std::abs`
* Remove SWIG macros
* Address unused-parameter warnings
* Address implicit-fallthrough warnings
* Address unused-variable warnings

Author: gmgunter

cxx/isce3/Headers.cmake

@@ -172,6 +172,14 @@ unwrap/icu/LabelMap.icc
 unwrap/icu/PhaseGrad.h
 unwrap/icu/SearchTable.h
 unwrap/icu/SearchTable.icc
+unwrap/ortools/ebert_graph.h
+unwrap/ortools/graph.h
+unwrap/ortools/graphs.h
+unwrap/ortools/iterators.h
+unwrap/ortools/max_flow.h
+unwrap/ortools/min_cost_flow.h
+unwrap/ortools/permutation.h
+unwrap/ortools/zvector.h
 unwrap/phass/ASSP.h
 unwrap/phass/BMFS.h
 unwrap/phass/CannyEdgeDetector.h

cxx/isce3/Sources.cmake

@@ -91,6 +91,8 @@ unwrap/icu/PhaseGrad.cpp
 unwrap/icu/Residue.cpp
 unwrap/icu/Tree.cpp
 unwrap/icu/Unwrap.cpp
+unwrap/ortools/max_flow.cc
+unwrap/ortools/min_cost_flow.cc
 unwrap/phass/ASSP.cc
 unwrap/phass/BMFS.cc
 unwrap/phass/CannyEdgeDetector.cc