moveUp method
Moves this node up in parent's children.
Implementation
bool moveUp() {
if (!hasParent) return false;
var parentRuntime = this.parentRuntime;
var idx = indexInParent;
if (idx < 0) return false;
if (idx == 0) return true;
remove();
var idxUp = parentRuntime!._contentFromIndexBackwardWhere(
idx - 1, 0, (node) => domGenerator.isElementNode(node));
if (idxUp < 0) {
idxUp = 0;
}
parentRuntime.insertAt(idxUp, node);
return true;
}