Blend modes (#252)

* Add backend for selecting layer blend mode

* Change dropdown input to support callback on change

* Add debug messages

* Fix canvas update for blend-modes

* Finish up and polish blend modes implementations

* Add changes from code review

Co-authored-by: Keavon Chambers <keavon@keavon.com>
Co-authored-by: Dennis Kobert <dennis@kobert.dev>

Cargo.lock

@@ -1,5 +1,7 @@
 # This file is automatically @generated by Cargo.
 # It is not intended for manual editing.
+version = 3
+
 [[package]]
 name = "aho-corasick"
 version = "0.7.18"
@@ -125,6 +127,7 @@ name = "graphite-wasm-wrapper"
 version = "0.1.0"
 dependencies = [
  "console_error_panic_hook",
+ "graphite-document-core",
  "graphite-editor-core",
  "log",
  "serde",