[ArrayManager] Enable pytables IO by falling back to BlockManager
This doesn't "fix" anything, but by falling back for now to the BlockManager-specific implementation of `to_hdf` writer, this avoids failures when using ArrayManager, which should make it easier to test it. 
@jorisvandenbossche only PRs for the rc are milestoned 1.3 for now to help track our readiness for the rc, otherwise they are milestone as they are merged.

Is this for the rc or can I remove the milestone for now? this is fine. @jorisvandenbossche can you open an issue for the impl in AM . It's mentioned as one of the bullet points in https://github.com/pandas-dev/pandas/issues/39146