官定机戦での駒の動きの候補一覧を算出する。
Ported https://github.com/sozysozbot/cerkeonlineutility/blob/master/src/calculatemovable.ts to Rust. See https://sites.google.com/view/cet2kaik/the-standardized-rule-in-english and https://github.com/sozysozbot/cerkeonline_utility for context.