date-time with default panics

[ahl]

This schema causes a panic:

    {
      "type": "object",
      "properties": {
        "when": {
          "type": "string",
          "format": "date-time",
          "default": "1970-01-01T00:00:00Z"
        }
      }
    }

"DateTime<chrono" is not a valid Ident

If we remove the default, it's fine. Why? This:

typify/typify-impl/src/value.rs

Lines 141 to 151 in 99ec168

	let text = value.to_string();
	let type_path = type_name
	.split("::")
	.map(|component| format_ident!("{}", component));
	// Deserialize the string to the type; the unwrap() is
	// unfortunate, but unavoidable without getting in the
	// underpants of the serialized form of these built-in types.
	quote! {
	serde_json::from_str::< #( #type_path )::* >(#text).unwrap()
	}

Instead we need to do what's done here:

typify/typify-impl/src/type_entry.rs

Lines 1617 to 1623 in 99ec168

	TypeEntryDetails::Native(TypeEntryNative {
	type_name: name, ..
	})
	| TypeEntryDetails::Integer(name)
	| TypeEntryDetails::Float(name) => syn::parse_str::<syn::TypePath>(name)
	.unwrap()
	.to_token_stream(),