Integrate the node graph as a Node Graph Frame layer type (#812)

* Add node graph frame tool

* Add a brighten

* Use the node graph

* Fix topological_sort

* Update UI

* Add icons for the tool and layer type

* Avoid serde & use bitmaps to improve performance

* Allow serialising a node graph

* Fix missing ..Default::default()

* Fix incorrect comments

* Cache node graph output image

* Suppress no-cycle import warning

Co-authored-by: Keavon Chambers <keavon@keavon.com>

node-graph/graph-craft/Cargo.toml

@@ -14,3 +14,8 @@ num-traits = "0.2"
 borrow_stack = { path = "../borrow_stack" }
 dyn-clone = "1.0"
 rand_chacha = "0.3.1"
+
+[dependencies.serde]
+version = "1.0"
+optional = true
+features = ["derive"]