Add 'Zoom with Scroll' input navigation scheme to preferences (#1021)

* Add use_scroll_as_zoom field to preference handler

* Add {Create,Delete}Mapping variants to message

* Revert "Add {Create,Delete}Mapping variants to message"

This reverts commit 0ba74754c9fb0c78d0b590c96e1d4fe2cfdd13e7.

* Revert "Add use_scroll_as_zoom field to preference handler"

This reverts commit d30f7c9edfa6d6e156939ca07f4db81f288975fd.

* Add basic scroll_as_zoom mapping

* Create overengineered mapping patch abstraction

* Add (for now passthrough) input layout manager

* Actually handle ModifyLayout messages (untested)

* Add backend preferences <-> layout manager comms

* Add scroll-as-zoom to actual preferences UI

* Rename LayoutManager -> KeyMapping

* Add Input section to preferences and title case

* Add scrollAsZoom frontend handling code (untested)

* Handle frontend <-> preferences comms

* (broken) Move scrollAsZoom persistence into state

* Fix scrollAsZoom having no effect on node graph

* Remove debugging helpers

* Fix confusion between horizontal and vertical

* Rename feature

* Move new message handler into folder

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

editor/src/messages/input_mapper/mod.rs

@@ -2,6 +2,7 @@ mod input_mapper_message;
 mod input_mapper_message_handler;
 
 pub mod default_mapping;
+pub mod key_mapping;
 pub mod utility_types;
 
 #[doc(inline)]