[WIP] [android] Run core unit tests in CI

[jfirebaugh]

Start to sketch how we'd run core unit tests on Android CI:

• Compile tests into a JNI lib
• Wrap with a simple Java main that calls into JNI
• Package as apk, upload and run on emulated device

[jfirebaugh]

Currently blocked by lacking gtest mason packaging for Android. Building it from source fails with:

In file included from src/gtest_main.cc:32:
In file included from ./include/gtest/gtest.h:58:
In file included from ./include/gtest/internal/gtest-internal.h:63:
./include/gtest/internal/gtest-type-util.h:73:14: error: no member named '__cxa_demangle' in namespace '__cxxabiv1'
  using abi::__cxa_demangle;
        ~~~~~^
./include/gtest/internal/gtest-type-util.h:75:31: error: use of undeclared identifier '__cxa_demangle'
  char* const readable_name = __cxa_demangle(name, 0, 0, &status);
                              ^
In file included from src/gtest-all.cc:39:
In file included from ./include/gtest/gtest.h:58:
In file included from ./include/gtest/internal/gtest-internal.h:63:
./include/gtest/internal/gtest-type-util.h:73:14: error: no member named '__cxa_demangle' in namespace '__cxxabiv1'
  using abi::__cxa_demangle;
        ~~~~~^
./include/gtest/internal/gtest-type-util.h:75:31: error: use of undeclared identifier '__cxa_demangle'
  char* const readable_name = __cxa_demangle(name, 0, 0, &status);
                              ^
2 errors generated.

[jfirebaugh]

Stale.