Support checking all files' text encodings, if declared to be UTF-8

Enforcing a specified text encoding in a monorepo rife with all kinds of textual resources is hard for crossplatform development teams. This feature would be of great value, and simple to implement. Especially if only a BOM-check is done. Alternatively, every text file that is covered by the EditorConfig settings can be decoded as UTF-8 on the fly.