[Ravenwood] Remove runtime-helper-src

Move all *_ravenwood classes into corresponding locations. Also move the
class load hook class into junit-impl.

Bug: 292141694
Flag: EXEMPT host side change only
Test: f/b/r/scripts/run-ravenwood-tests.sh
Change-Id: I95aa7dac3c30de0440de2b4c07cc39c29302ed9c