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>

document-legacy/Cargo.toml

@@ -21,6 +21,7 @@ bezier-rs = { path = "../libraries/bezier-rs" }
 kurbo = { git = "https://github.com/linebender/kurbo.git", features = [
 	"serde",
 ] }
+specta.workspace = true
 serde = { version = "1.0", features = ["derive"] }
 base64 = "0.13"
 glam = { version = "0.22", features = ["serde"] }