Update ExtensionType trait to support more canonical extension types

Author: mbrobbel

arrow-schema/Cargo.toml

@@ -34,13 +34,19 @@ path = "src/lib.rs"
 bench = false
 
 [dependencies]
-serde = { version = "1.0", default-features = false, features = ["derive", "std", "rc"], optional = true }
+serde = { version = "1.0", default-features = false, features = [
+    "derive",
+    "std",
+    "rc",
+], optional = true }
 bitflags = { version = "2.0.0", default-features = false, optional = true }
-serde_json = "1.0"
+serde_json = { version = "1.0", optional = true }
 
 [features]
+canonical-extension-types = ["dep:serde", "dep:serde_json"]
 # Enable ffi support
 ffi = ["bitflags"]
+serde = ["dep:serde"]
 
 [package.metadata.docs.rs]
 features = ["ffi"]