Add `HasSafeVersion{E,B}` classes for the safe/unsafe conversion bridge.
Add `HasSafeVersion{E,B}` classes for the safe/unsafe conversion bridge.

google-research/dex-lang,google-research/dex-lang,google-research/dex-lang,google-research/dex-lang,google-research/dex-lang,google-research/dex-lang