elideComment = node => {
  if (node.type === 'CommentBlock') {
    if (!markedForPreservation(node.value)) {
      node.value = node.value.replace(/[^\n]+\n/g, '\n').replace(/[^\n]/g, ' ');
    }
  } else {
    node.value = '';
  }
}
Elides all non-newlines before the last line and replaces all non-newlines
with spaces on the last line.
This can greatly reduce the size of a well-commented artifact without
displacing lines or columns in the transformed code.

@param {import('@babel/types').Comment} node