Switch facebook-www build version to file content hash (#28633)

Unifies the React version string pattern with RN just to simplify the
build script a tiny bit and not have 2 mechanisms for the Meta-internal
build.

scripts/rollup/build-all-release-channels.js

@@ -158,18 +158,16 @@ function processStable(buildDir) {
   }
 
   if (fs.existsSync(buildDir + '/facebook-www')) {
-    const hash = crypto.createHash('sha1');
     for (const fileName of fs.readdirSync(buildDir + '/facebook-www').sort()) {
       const filePath = buildDir + '/facebook-www/' + fileName;
       const stats = fs.statSync(filePath);
       if (!stats.isDirectory()) {
-        hash.update(fs.readFileSync(filePath));
         fs.renameSync(filePath, filePath.replace('.js', '.classic.js'));
       }
     }
     updatePlaceholderReactVersionInCompiledArtifacts(
       buildDir + '/facebook-www',
-      ReactVersion + '-www-classic-' + hash.digest('hex').slice(0, 8)
+      ReactVersion + '-www-classic-%FILEHASH%'
     );
   }
 
@@ -224,18 +222,16 @@ function processExperimental(buildDir, version) {
   }
 
   if (fs.existsSync(buildDir + '/facebook-www')) {
-    const hash = crypto.createHash('sha1');
     for (const fileName of fs.readdirSync(buildDir + '/facebook-www').sort()) {
       const filePath = buildDir + '/facebook-www/' + fileName;
       const stats = fs.statSync(filePath);
       if (!stats.isDirectory()) {
-        hash.update(fs.readFileSync(filePath));
         fs.renameSync(filePath, filePath.replace('.js', '.modern.js'));
       }
     }
     updatePlaceholderReactVersionInCompiledArtifacts(
       buildDir + '/facebook-www',
-      ReactVersion + '-www-modern-' + hash.digest('hex').slice(0, 8)
+      ReactVersion + '-www-modern-%FILEHASH%'
     );
   }