Extract StackReuseCodegen tests.

test/libyul/evmCodeTransform/stackReuse/reuse_slots.yul

@@ -0,0 +1,23 @@
+{ let a, b, c, d let x := 2 let y := 3 mstore(x, a) mstore(y, c) }
+// ====
+// stackOptimization: true
+// ----
+// PUSH1 0x0
+// PUSH1 0x0
+// PUSH1 0x0
+// PUSH1 0x0
+// POP
+// PUSH1 0x2
+// SWAP2
+// POP
+// PUSH1 0x3
+// DUP4
+// DUP4
+// MSTORE
+// DUP2
+// DUP2
+// MSTORE
+// POP
+// POP
+// POP
+// POP