Add the ability to emulate the old svn_fs_paths_changed2 through svn_fs_paths_changed3. So, we've got a two-way emulation now and we enable both for now such that all callers of the old API will be redirected: old API -> new API -> old API vtable entry.
As a bonus, the emulated svn_fs_paths_changed2 now correctly reports the IDs for in-revision nodes in FSFS. It also fails earlier on corrupted change lists. Both is only true for "emulated" mode.
* subversion/include/private/svn_fs_util.h (svn_fs__get_deleted_node): Declare a new private utility API needed to handle ID creation edge cases.
* subversion/libsvn_fs/fs-loader.c (SVN_FS_EMULATE_PATHS_CHANGED): Declare new control macro as we did already for the new API. (add_changed_path_baton_t, add_changed_path): Callback implementation to emulate the old API based on the new one. (svn_fs_paths_changed2): Emulate when necessary or forced to do so.
* subversion/tests/cmdline/svnadmin_tests.py (verify_invalid_path_changes): The correct ID construction in emulated mode creates fewer repetitions of the same error during verification. Update test expectations accordingly.