Add Java SimpleIterator goody

[miorel]

This makes it easy to implement an Iterator while providing only a next() method. The hasNext() method is then filled in for you via the toIterator method.

[github-actions]

PR Health Report

Last checked commit cb64b04.

• npx prettier --write .github .vscode && ! (git status --porcelain | grep .): ✅
• (cd tools && yarn format && ! (git status --porcelain | grep .)): ✅
• (cd tools && yarn lint): ✅
• (cd tools && yarn typecheck): ✅
• (cd tools && yarn test): ✅
• (cd tools/adventure-pack && yarn build-app): ✅