refactor overseer into proc-macro based pattern (#2962)

polkadot/node/overseer/all-subsystems-gen/tests/ui/ok-01-w-generics.rs

@@ -0,0 +1,17 @@
+#![allow(dead_code)]
+
+use polkadot_overseer_all_subsystems_gen::AllSubsystemsGen;
+
+#[derive(Clone, AllSubsystemsGen)]
+struct AllSubsystems<A, B> {
+	a: A,
+	b: B,
+}
+
+fn main() {
+	let all = AllSubsystems::<u8, u16> {
+		a: 0u8,
+		b: 1u16,
+	};
+	let _all: AllSubsystems<_,_> = all.replace_a::<u32>(777_777u32);
+}