[syntax] Lower empty jsx attributes to true

--- 

Found when enabling Forget for webamp 

``` 

% yarn sprout --filter --verbose 

yarn run v1.22.19 

$ node ../sprout/dist/main.js --filter --verbose 

PASS  jsx-attribute-default-to-true 

ok <div>{"truthyAttribute":true}</div> 

1 Tests, 1 Passed, 0 Failed 

✨  Done in 2.45s. 

```

compiler/packages/babel-plugin-react-forget/src/HIR/BuildHIR.ts

@@ -1927,6 +1927,12 @@ function lowerExpression(
         let value;
         if (valueExpr.isJSXElement() || valueExpr.isStringLiteral()) {
           value = lowerExpressionToTemporary(builder, valueExpr);
+        } else if (valueExpr.type == null) {
+          value = lowerValueToTemporary(builder, {
+            kind: "Primitive",
+            value: true,
+            loc: attribute.node.loc ?? GeneratedSource,
+          });
         } else {
           if (!valueExpr.isJSXExpressionContainer()) {
             builder.errors.push({

compiler/packages/babel-plugin-react-forget/src/__tests__/fixtures/compiler/jsx-attribute-default-to-true.expect.md

@@ -0,0 +1,43 @@
+
+## Input
+
+```javascript
+import { Stringify } from "shared-runtime";
+
+function Component() {
+  // https://legacy.reactjs.org/docs/jsx-in-depth.html#props-default-to-true
+  return <Stringify truthyAttribute />;
+}
+
+export const FIXTURE_ENTRYPOINT = {
+  fn: Component,
+  params: [{}],
+};
+
+```
+
+## Code
+
+```javascript
+import { unstable_useMemoCache as useMemoCache } from "react";
+import { Stringify } from "shared-runtime";
+
+function Component() {
+  const $ = useMemoCache(1);
+  let t0;
+  if ($[0] === Symbol.for("react.memo_cache_sentinel")) {
+    t0 = <Stringify truthyAttribute={true} />;
+    $[0] = t0;
+  } else {
+    t0 = $[0];
+  }
+  return t0;
+}
+
+export const FIXTURE_ENTRYPOINT = {
+  fn: Component,
+  params: [{}],
+};
+
+```
+      

compiler/packages/babel-plugin-react-forget/src/__tests__/fixtures/compiler/jsx-attribute-default-to-true.tsx

@@ -0,0 +1,11 @@
+import { Stringify } from "shared-runtime";
+
+function Component() {
+  // https://legacy.reactjs.org/docs/jsx-in-depth.html#props-default-to-true
+  return <Stringify truthyAttribute />;
+}
+
+export const FIXTURE_ENTRYPOINT = {
+  fn: Component,
+  params: [{}],
+};

compiler/packages/babel-plugin-react-forget/src/__tests__/fixtures/tsconfig.json

@@ -4,6 +4,7 @@
 {
   "compilerOptions": {
     "allowJs": true,
+    "isolatedModules": true,
     "noEmit": true,
     "noImplicitAny": false,
     "noUncheckedIndexedAccess": false,

compiler/packages/sprout/src/shared-runtime.ts

@@ -135,6 +135,7 @@ export function Text(props: {
   return React.createElement("div", null, props.value, props.children);
 }
 
+
 export function StaticText1(props: { children?: Array<React.ReactNode> }) {
   return React.createElement("div", null, "StaticText1", props.children);
 }
@@ -154,8 +155,12 @@ export function RenderPropAsChild(props: {
   );
 }
 
-export function Stringify(props: any) {
-  return toJSON(props);
+export function Stringify(props: any): React.ReactElement {
+  return React.createElement(
+    "div",
+    null,
+    toJSON(props),
+  );
 }
 
 // helper functions