Fix FBT whitespace handling (again (again))

Nice find, @mofeiZ! I really tried to thoroughly test all the examples I could 
think of for FBT whitespace but i missed the newline case. Initially Mofei found 
[this code potentially related to whitespace 
handling](https://github.com/facebook/fbt/blob/main/packages/babel-plugin-fbt/src/fbt-nodes/FbtImplicitParamNode.js#L230-L233) 
but Babel never seems to produce consecutive JsxText nodes — this looks like 
maybe a leftover from older babel versions. 

I noticed that code wasn't actually trimming the whitspace but clearly it was 
happening somewhere, so i grepped for 'trim' and found that [this 
code](https://github.com/facebook/fbt/blob/0b4e0d13c30bffd0daa2a75715d606e3587b4e40/packages/babel-plugin-fbt/src/babel-processors/JSXFbtProcessor.js#L143) 
calls a 
[normalizeSpaces](https://github.com/facebook/fbt/blob/0b4e0d13c30bffd0daa2a75715d606e3587b4e40/packages/babel-plugin-fbt/src/FbtUtil.js#L86C10-L86C45) 
helper. Updating our logic to handle whitespace similarly just for children of 
fbt nodes produces the expected result.

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

@@ -1902,10 +1902,6 @@ function lowerExpression(
       const expr = exprPath as NodePath<t.JSXElement>;
       const opening = expr.get("openingElement");
       const tag = lowerJsxElementName(builder, opening.get("name"));
-      const children: Array<Place> = expr
-        .get("children")
-        .map((child) => lowerJsxElement(builder, child))
-        .filter(notNull);
       const props: Array<JsxAttribute> = [];
       for (const attribute of opening.get("attributes")) {
         if (attribute.isJSXSpreadAttribute()) {
@@ -1982,6 +1978,32 @@ function lowerExpression(
         }
         props.push({ kind: "JsxAttribute", name: propName, place: value });
       }
+      let children: Array<Place>;
+      if (tag.kind === "BuiltinTag" && tag.name === "fbt") {
+        children = expr
+          .get("children")
+          .map((child) => {
+            if (child.isJSXText()) {
+              /*
+               * FBT whitespace normalization differs from standard JSX:
+               * https://github.com/facebook/fbt/blob/0b4e0d13c30bffd0daa2a75715d606e3587b4e40/packages/babel-plugin-fbt/src/FbtUtil.js#L76-L87
+               */
+              const text = child.node.value.replace(/[^\S\u00A0]+/g, " ");
+              return lowerValueToTemporary(builder, {
+                kind: "JSXText",
+                value: text,
+                loc: exprLoc,
+              });
+            }
+            return lowerJsxElement(builder, child);
+          })
+          .filter(notNull);
+      } else {
+        children = expr
+          .get("children")
+          .map((child) => lowerJsxElement(builder, child))
+          .filter(notNull);
+      }
       return {
         kind: "JsxExpression",
         tag,

compiler/packages/babel-plugin-react-forget/src/__tests__/fixtures/compiler/fbt-preserve-whitespace.expect.md

@@ -3,10 +3,8 @@
 
 ```javascript
 import fbt from "fbt";
-/**
- * TODO: remove this from SproutTodoFilter when fixed.
- */
 
+const _ = fbt;
 function Component({ value }: { value: string }) {
   return (
     <fbt desc="descdesc">
@@ -28,17 +26,15 @@ export const FIXTURE_ENTRYPOINT = {
 ```javascript
 import { unstable_useMemoCache as useMemoCache } from "react";
 import fbt from "fbt";
-/**
- * TODO: remove this from SproutTodoFilter when fixed.
- */
 
-function Component(t11) {
+const _ = fbt;
+function Component(t12) {
   const $ = useMemoCache(2);
-  const { value } = t11;
+  const { value } = t12;
   let t0;
   if ($[0] !== value) {
     t0 = fbt._(
-      "Before text{paramName}",
+      "Before text {paramName}",
       [
         fbt._param(
           "paramName",
@@ -46,7 +42,7 @@ function Component(t11) {
           value
         ),
       ],
-      { hk: "3DIRxJ" }
+      { hk: "3z5SVE" }
     );
     $[0] = value;
     $[1] = t0;

compiler/packages/babel-plugin-react-forget/src/__tests__/fixtures/compiler/fbt-preserve-whitespace.tsx

@@ -1,8 +1,6 @@
 import fbt from "fbt";
-/**
- * TODO: remove this from SproutTodoFilter when fixed.
- */
 
+const _ = fbt;
 function Component({ value }: { value: string }) {
   return (
     <fbt desc="descdesc">

compiler/packages/babel-plugin-react-forget/src/__tests__/fixtures/compiler/fbtparam-with-jsx-element-content.expect.md

@@ -28,9 +28,9 @@ function Component({ name, data, icon }) {
 import { unstable_useMemoCache as useMemoCache } from "react";
 import fbt from "fbt";
 
-function Component(t29) {
+function Component(t33) {
   const $ = useMemoCache(4);
-  const { name, data, icon } = t29;
+  const { name, data, icon } = t33;
   let t0;
   if ($[0] !== name || $[1] !== icon || $[2] !== data) {
     t0 = (

compiler/packages/sprout/src/SproutTodoFilter.ts

@@ -469,7 +469,6 @@ const skipFilter = new Set([
 
   // Bug in Forget output
   "todo-rename-source-variables",
-  "bug-fbt-preserve-whitespace",
 
   // Tested e2e in forget-feedback repo
   "userspace-use-memo-cache",