Implement the Brush without relying on a stamp texture

Test Plan: Test the BrushNode in the editor

Reviewers: Keavon

Reviewed By: Keavon

Pull Request: https://github.com/GraphiteEditor/Graphite/pull/1184

node-graph/gcore/src/structural.rs

@@ -81,7 +81,7 @@ mod test {
 	fn test_ref_eval() {
 		let value = ValueNode::new(5);
 
-		assert_eq!((&value).eval(()), &5);
+		assert_eq!(value.eval(()), &5);
 		let id = IdNode::new();
 
 		let compose = ComposeNode::new(&value, &id);