[λ] Re run SSA on function expr

Functions can capture variables declared after the definition of the function. 
This re runs SSA to map the captured identifiers to the new SSA identifiers if 
available.

compiler/forget/src/SSA/EnterSSA.ts

@@ -226,4 +226,12 @@ export default function enterSSA(func: HIRFunction) {
       }
     }
   }
+
+  for (const [_, block] of func.body.blocks) {
+    for (const instr of block.instructions) {
+      if (instr.value.kind === "FunctionExpression") {
+        mapInstructionOperands(instr, (place) => builder.getPlace(place));
+      }
+    }
+  }
 }

compiler/forget/src/__tests__/fixtures/hir/mutate-captured-arg-separately.expect.md

@@ -0,0 +1,38 @@
+
+## Input
+
+```javascript
+function component(a) {
+  let y = function () {
+    m(x);
+  };
+
+  let x = { a };
+  m(x);
+  return y;
+}
+
+```
+
+## Code
+
+```javascript
+function component(a) {
+  const $ = React.useMemoCache();
+  let y;
+  if ($[0] === Symbol.for("react.memo_cache_sentinel")) {
+    y = function () {
+      m(x);
+    };
+    $[0] = y;
+  } else {
+    y = $[0];
+  }
+
+  const x = { a: a };
+  m(x);
+  return y;
+}
+
+```
+      

compiler/forget/src/__tests__/fixtures/hir/mutate-captured-arg-separately.js

@@ -0,0 +1,9 @@
+function component(a) {
+  let y = function () {
+    m(x);
+  };
+
+  let x = { a };
+  m(x);
+  return y;
+}