[HostStubGen] Improve class load and method call hooks

- Instead of going through a trampoline in HostTestUtils, make hsg
  generate bytecode to directly call the hook methods.
- Add new tests for method call hooks.
- Remove the "ext" variant of tiny-framework, always enable the default
  class load hook and method call hooks.
- Make sure ProcessAsKeep annotation is only injected when the method is
  marked as "@Keep"

Bug: 292141694
Flag: EXEMPT host side change only
Test: f/b/r/scripts/run-ravenwood-tests.sh
Change-Id: Ie09762c7b869507d2103e6a9b270d9edc3a32998