Parachain validation moved to external process (#325)

* Improved execution & tests

* Style

* Made CLI arg const

* Moved Upwards message

* CLI subcommand for validation worker

* Build halting parachain

* Build halting parachain

* Made stuff private

* Reorganized parachain tests

* Comment

* Whitespace

* Apply suggestions from code review

Co-Authored-By: Bastian Köcher <bkchr@users.noreply.github.com>

* Fixed call data size check and introduced an enum

* Apply suggestions from code review

Co-Authored-By: Bastian Köcher <bkchr@users.noreply.github.com>

polkadot/parachain/src/lib.rs

@@ -207,3 +207,13 @@ pub struct UpwardMessageRef<'a> {
 	/// Underlying data of the message.
 	pub data: &'a [u8],
 }
+
+/// A message from a parachain to its Relay Chain.
+#[derive(Clone, PartialEq, Eq, Encode, Decode)]
+#[cfg_attr(feature = "std", derive(Debug))]
+pub struct UpwardMessage {
+	/// The origin for the message to be sent from.
+	pub origin: ParachainDispatchOrigin,
+	/// The message data.
+	pub data: Vec<u8>,
+}