Add the OpenROAD C++ tests to BUILD

[mithro]

It would be good is the OpenROAD build file included the various OpenROAD C++ tests being built and run.

Probably best to start with the tests using gtest;

src/cts/test/cts_unittest.cc:#include "gtest/gtest.h"
src/gpl/test/fft_test.cc:#include "gtest/gtest.h"
src/dft/test/cpp/TestScanArchitectHeuristic.cpp:#include "gtest/gtest.h"
src/dft/test/cpp/TestScanArchitect.cpp:#include "gtest/gtest.h"
src/dpl/test/dpl_test.cc:#include "gtest/gtest.h"
src/mpl2/test/cpp/mpl2_test.cc:#include "gtest/gtest.h"
src/odb/test/cpp/TestAbstractLef.cc:#include "gtest/gtest.h"
src/odb/test/cpp/TestDbWire.cc:#include "gtest/gtest.h"
src/odb/test/cpp/sky130_test_fixture.h:#include "gtest/gtest.h"

[mithro]

Once we upgrade to a version which has my new fft_test landed in The-OpenROAD-Project/OpenROAD#4518 I'll look at adding that.