libadf: convert to C++

Both humans and the clang static analyzer find libadf's error handling
confusing.

Now that the platform has better C++ support, we can clean up things up
by switching to C++ and using STL + RAII in targeted parts of the code.
This isn't a complete rewrite in idiomatic C++, but it's enough to get
rid of all the "goto" statements (and the false-positive memory leaks
found by clang's static analyzer).

Bug: 27125399

Test: WITH_STATIC_ANALYZER=1 mmm system/core/adf/libadf
Test: /data/nativetest/adf-unit-tests/adf-unit-tests (on Nexus 9)
Test: /data/nativetest64/adf-unit-tests/adf-unit-tests (on Nexus 9)
Change-Id: Ie9dd5d5dc424d1a3ddcc3cba836fce04190f46fd
Signed-off-by: Greg Hackmann <ghackmann@google.com>