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/set_empty_storage.wat

@@ -0,0 +1,15 @@
+;; This module stores a KV pair into the storage
+(module
+	(import "seal0" "seal_set_storage" (func $seal_set_storage (param i32 i32 i32)))
+	(import "env" "memory" (memory 16 16))
+
+	(func (export "call")
+	)
+	(func (export "deploy")
+		(call $seal_set_storage
+			(i32.const 0)				;; Pointer to storage key
+			(i32.const 0)				;; Pointer to value
+			(i32.load (i32.const 0))	;; Size of value
+		)
+	)
+)