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/chain_extension.wat

@@ -0,0 +1,46 @@
+;; Call chain extension by passing through input and output of this contract
+(module
+	(import "seal0" "call_chain_extension"
+		(func $call_chain_extension (param i32 i32 i32 i32 i32) (result i32))
+	)
+	(import "seal0" "seal_input" (func $seal_input (param i32 i32)))
+	(import "seal0" "seal_return" (func $seal_return (param i32 i32 i32)))
+	(import "env" "memory" (memory 16 16))
+
+	(func $assert (param i32)
+		(block $ok
+			(br_if $ok (get_local 0))
+			(unreachable)
+		)
+	)
+
+	;; [0, 4) len of input output
+	(data (i32.const 0) "\08")
+
+	;; [4, 12) buffer for input
+
+	;; [12, 48) len of output buffer
+	(data (i32.const 12) "\20")
+
+	;; [16, inf) buffer for output
+
+	(func (export "deploy"))
+
+	(func (export "call")
+		(call $seal_input (i32.const 4) (i32.const 0))
+
+		;; the chain extension passes through the input and returns it as output
+		(call $call_chain_extension
+			(i32.load (i32.const 4))	;; id
+			(i32.const 4)				;; input_ptr
+			(i32.load (i32.const 0))	;; input_len
+			(i32.const 16)				;; output_ptr
+			(i32.const 12)				;; output_len_ptr
+		)
+
+		;; the chain extension passes through the id
+		(call $assert (i32.eq (i32.load (i32.const 4))))
+
+		(call $seal_return (i32.const 0) (i32.const 16) (i32.load (i32.const 12)))
+	)
+)