Ravenizer tool skelton

- It still doesn't do any conversion, but the outer structure is done.
- Also make the "load class structure" step a bit faster by loading
    classes in parallel.

Flag: EXEMPT host test change only
Bug: 360390999
Test: $ANDROID_BUILD_TOP/frameworks/base/ravenwood/scripts/run-ravenwood-tests.sh
Change-Id: I0f28ccd7388c310f0f733900fea9ad709e16f1cb