Contracts move fixtures to new crate (#2246)

Small PR that introduce a new crate that will host RISC-V & wasm
fixtures for testing pallet-contracts

substrate/frame/contracts/fixtures/data/self_destructing_constructor.wat

@@ -0,0 +1,23 @@
+(module
+	(import "seal0" "seal_terminate" (func $seal_terminate (param i32 i32)))
+	(import "env" "memory" (memory 1 1))
+
+	(func $assert (param i32)
+		(block $ok
+			(br_if $ok
+				(get_local 0)
+			)
+			(unreachable)
+		)
+	)
+
+	(func (export "deploy")
+		;; Self-destruct by sending full balance to the 0 address.
+		(call $seal_terminate
+			(i32.const 0)	;; Pointer to destination address
+			(i32.const 32)	;; Length of destination address
+		)
+	)
+
+	(func (export "call"))
+)