Groundwork for integrating Specta (#949)

* add derive(specta::Type)

* use specta from git

* introduce Uuid type

* remove unnecessary specta::Type

* document export_types test

* upgrade Specta
The previous Specta branch had some hacks that were just for this project. They have all been converted into proper features so they can be merged into main.

* remove some unnecessary specta::Type uses

* add MessageDiscriminantDef explanation

* manually export types with specta

* rename 'specta.rs' to 'export_types.rs'

* rename 'export_types' to 'generate_ts_types'

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Co-authored-by: Oscar Beaumont <oscar@otbeaumont.me>

node-graph/gcore/Cargo.toml

@@ -33,4 +33,5 @@ kurbo = { git = "https://github.com/linebender/kurbo.git", features = [
 ], optional = true }
 glam = { version = "^0.22", default-features = false, features = ["scalar-math", "libm"]}
 node-macro = {path = "../node-macro"}
+specta.workspace = true
 # forma = { version = "0.1.0", package = "forma-render" }