SPM: fix raw Flow type annotations in bare-node scripts (#57660)

Summary:
The scripts under `packages/react-native/scripts/spm/` are executed as plain `node` (via `setup-apple-spm.js` during the SwiftPM Xcode build), with **no Babel** to strip Flow. They use Flow-in-comment syntax (`/*: T */`) throughout so they parse un-transpiled.

A handful of uninitialized `let X: T;` declarations had slipped in with **raw** Flow annotations. Node parses the whole file on `require`, so each one throws `SyntaxError: Unexpected token ':'` at load time — taking the entire module down before it can run.

The jest suites didn't catch it because jest runs these files through `react-native/babel-preset`, which strips raw and comment-form annotations alike. Only the bare-`node` shipped path (SwiftPM setup) hits the error.

## Fix

Convert each offending declaration to Flow-comment form. Prettier's `flow` parser only keeps a comment type attached to the binding when the declaration is **initialized**, so each site gets a type-appropriate (inert) initializer — every variable is reassigned in the immediately-following `try`/branch before any use:

| file | lines | form |
|---|---|---|
| `autolinking-plugins.js` | 120, 178 | `/*: unknown */ = undefined` |
| `download-spm-artifacts.js` | 946, 973 | `/*: string */ = ''` |
| `download-spm-artifacts.js` | 1352 | `/*: {...} */ = {}` |
| `generate-spm-autolinking.js` | 429 | `/*: Array<...> */ = []` |
| `generate-spm-xcodeproj.js` | 1802 | `/*: string */ = ''` |
| `generate-spm-xcodeproj.js` | 1808 | `/*: unknown */ = undefined` |
| `generate-spm-xcodeproj.js` | 1863 | `/*: Array<...> */ = []` |
| `scaffold-package-swift.js` | 200, 1129 | `/*: Array<...> */ = []` |
| `scaffold-package-swift.js` | 933 | annotation dropped — Flow infers `PodspecModel` from `readPodspec()` |

## Changelog:
[INTERNAL] [FIXED] - Fix raw Flow type annotations that broke bare-node execution of the SwiftPM setup scripts

Pull Request resolved: #57660

Test Plan:
- `node --check` passes on all 14 `scripts/spm/*.js` (previously `autolinking-plugins.js` and `download-spm-artifacts.js` threw `SyntaxError` at parse time).
- `flow focus-check` reports **0 errors** in the touched files.
- Prettier: clean.
- SPM jest suites: green.

## Changelog:

[INTERNAL] [FIXED] - Fix raw Flow type annotations that broke bare-node execution of the SwiftPM setup scripts

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Reviewed By: cortinico

Differential Revision: D113554595

Pulled By: cipolleschi

fbshipit-source-id: b7fa29dd54266b749e1671333fb0530f6b6a8aab

Author: chrfalch

packages/react-native/scripts/spm/autolinking-plugins.js

@@ -117,7 +117,7 @@ function discoverPlugins(
       );
     }
     const pluginPath = path.resolve(dep.root, rel);
-    let fn: unknown;
+    let fn /*: unknown */ = null;
     try {
       // $FlowFixMe[unsupported-syntax] dynamic require by computed path
       fn = require(pluginPath);
@@ -175,7 +175,7 @@ function invokePlugins(
   const seenFrameworkNames /*: Set<string> */ = new Set();
 
   for (const {depName, pluginPath, plugin} of plugins) {
-    let result: unknown;
+    let result /*: unknown */ = null;
     try {
       result = plugin(context);
     } catch (e) {

packages/react-native/scripts/spm/download-spm-artifacts.js

@@ -943,7 +943,7 @@ async function processArtifact(
     return localPath;
   };
 
-  let tarPath: string;
+  let tarPath /*: string */ = '';
   let fromShared = false;
   if (isLocalTarball) {
     tarPath = url;
@@ -970,7 +970,7 @@ async function processArtifact(
     onProgress(xcframeworkName, 0, 0, 0, false, 0);
   }
   const tmpExtractDir = path.join(outputDir, '.extract-tmp', label);
-  let xcfwPath: string;
+  let xcfwPath /*: string */ = '';
   try {
     xcfwPath = extractXCFramework(tarPath, tmpExtractDir);
   } catch (e) {
@@ -1349,7 +1349,7 @@ function validateArtifactsCache(
   if (!fs.existsSync(artifactsJsonPath)) {
     return `artifacts.json missing in ${artifactsDir}`;
   }
-  let json: {[string]: {xcframeworkPath: string, url: string}};
+  let json /*: {[string]: {xcframeworkPath: string, url: string}} */ = {};
   try {
     // $FlowFixMe[unclear-type] JSON.parse returns any
     const parsed /*: any */ = JSON.parse(

packages/react-native/scripts/spm/generate-spm-autolinking.js

@@ -426,7 +426,7 @@ function hasMixedLanguageSources(absSource /*: string */) /*: boolean */ {
   let hasClang = false;
   const walk = (dir /*: string */, depth /*: number */) => {
     if (depth > 6 || (hasSwift && hasClang)) return;
-    let entries: Array<{name: string, isDirectory(): boolean}>;
+    let entries /*: Array<{name: string, isDirectory(): boolean}> */ = [];
     try {
       // $FlowFixMe[incompatible-type] Dirent typing
       entries = fs.readdirSync(dir, {withFileTypes: true});

packages/react-native/scripts/spm/generate-spm-xcodeproj.js

@@ -1799,13 +1799,13 @@ function readGeneratedSourcesManifest(
   appRoot /*: string */,
 ) /*: Array<GeneratedSource> */ {
   const manifestPath = path.join(appRoot, SPM_GENERATED_SOURCES_MANIFEST);
-  let raw: string;
+  let raw /*: string */ = '';
   try {
     raw = fs.readFileSync(manifestPath, 'utf8');
   } catch {
     return [];
   }
-  let entries: unknown;
+  let entries /*: unknown */ = null;
   try {
     entries = JSON.parse(raw);
   } catch {
@@ -1860,7 +1860,7 @@ function readMarker(
 // build-time sync (sync-spm-autolinking.js, via readArtifactsVersionOverride
 // below) to call without pulling in any pbxproj-editing machinery at runtime.
 function findInjectedXcodeproj(appRoot /*: string */) /*: string | null */ {
-  let entries: Array<{name: string, isDirectory(): boolean}>;
+  let entries /*: Array<{name: string, isDirectory(): boolean}> */ = [];
   try {
     // $FlowFixMe[incompatible-type] Dirent typing
     entries = fs.readdirSync(appRoot, {withFileTypes: true});

packages/react-native/scripts/spm/scaffold-package-swift.js

@@ -197,7 +197,7 @@ function collectSubdirs(
   ]);
   const out /*: Array<string> */ = [];
   const walk = (absDir /*: string */, relDir /*: string */) => {
-    let entries: Array<{name: string, isDirectory(): boolean}>;
+    let entries /*: Array<{name: string, isDirectory(): boolean}> */ = [];
     try {
       // $FlowFixMe[incompatible-type] Dirent typing
       entries = fs.readdirSync(absDir, {withFileTypes: true});
@@ -930,7 +930,7 @@ function scaffoldPackageSwiftForDep(
     };
   }
 
-  let model: PodspecModel;
+  let model;
   try {
     model = readPodspec(podspecPath);
   } catch (e) {
@@ -1126,7 +1126,7 @@ function scaffoldAll(
     directDeps.push({name, root, platforms: {ios: iosPlatform}});
   }
 
-  let allDeps: Array<AutolinkedDep>;
+  let allDeps /*: Array<AutolinkedDep> */ = [];
   try {
     allDeps = expandSpmDependencies(directDeps, {
       readConfig: defaultReadConfig,