Please modify all BlockLegacy::mayPlace to BlockSource::mayPlace.

I think in the right situation, all actions that destroy blocks should be handled by BlockSource::mayPlace, but some use BlockLegacy::mayPlace. And the latter did not return the Actor pointer, which caused me trouble to write plug-ins. In fact, BlockSource::mayPlace should be used for all destructive behaviors. Please modify it, for BDS, thank you.