Fixture for reassignment within value block

Fixture from T175283039, a reassignment within an expression can sometimes 
generate a StoreLocal within a value block. Depending on the case this can end 
up as the last instruction of the block, which then hits an invariant.

compiler/packages/babel-plugin-react-forget/src/__tests__/fixtures/compiler/error.todo-reassign-in-while-loop-condition.expect.md

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+
+## Input
+
+```javascript
+import { makeArray } from "shared-runtime";
+
+// @flow
+function Component() {
+  const items = makeArray(0, 1, 2);
+  let item;
+  let sum = 0;
+  while ((item = items.pop())) {
+    sum += item;
+  }
+  return [sum];
+}
+
+export const FIXTURE_ENTRYPOINT = {
+  fn: Component,
+  params: [{}],
+};
+
+```
+
+
+## Error
+
+```
+   6 |   let item;
+   7 |   let sum = 0;
+>  8 |   while ((item = items.pop())) {
+     |           ^^^^ [ReactForget] Invariant: Unexpected StoreLocal in codegenInstructionValue (8:8)
+   9 |     sum += item;
+  10 |   }
+  11 |   return [sum];
+```
+          
+      

compiler/packages/babel-plugin-react-forget/src/__tests__/fixtures/compiler/error.todo-reassign-in-while-loop-condition.js

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+import { makeArray } from "shared-runtime";
+
+// @flow
+function Component() {
+  const items = makeArray(0, 1, 2);
+  let item;
+  let sum = 0;
+  while ((item = items.pop())) {
+    sum += item;
+  }
+  return [sum];
+}
+
+export const FIXTURE_ENTRYPOINT = {
+  fn: Component,
+  params: [{}],
+};