Add another Gulp task to fetch all platform packages

We fetch these from an upstream feed that has authenticated feeds
as upstreams of it; this is an easy way to ensure everything is
cached properly for all platforms.

tasks/offlinePackagingTasks.ts

@@ -73,8 +73,43 @@ gulp.task('installDependencies', async () => {
     }
 });
 
+gulp.task('fetchAllRoslynPlatformPackages', async () => {
+    const packageJSON = getPackageJSON();
+
+    // Fetch the neutral package that we don't otherwise have in our platform list
+    await acquireRoslyn(packageJSON, undefined);
+
+    // And now fetch each platform specific
+    for (const p of platformSpecificPackages) {
+        await acquireRoslyn(packageJSON, p.platformInfo);
+    }
+});
+
 // Install Tasks
 async function installRoslyn(packageJSON: any, platformInfo?: PlatformInformation) {
+    const { packagePath, serverPlatform } = await acquireRoslyn(packageJSON, platformInfo);
+
+    // Get the directory containing the server executable for the current platform.
+    const serverExecutableDirectory = path.join(packagePath, 'content', 'LanguageServer', serverPlatform);
+    if (!fs.existsSync(serverExecutableDirectory)) {
+        throw new Error(`Failed to find server executable directory at ${serverExecutableDirectory}`);
+    }
+
+    console.log(`Extracting Roslyn executables from ${serverExecutableDirectory}`);
+
+    // Copy the files to the language server directory.
+    fs.mkdirSync(languageServerDirectory);
+    fsextra.copySync(serverExecutableDirectory, languageServerDirectory);
+    const languageServerDll = path.join(languageServerDirectory, 'Microsoft.CodeAnalysis.LanguageServer.dll');
+    if (!fs.existsSync(languageServerDll)) {
+        throw new Error(`Failed to copy server executable`);
+    }
+}
+
+async function acquireRoslyn(
+    packageJSON: any,
+    platformInfo?: PlatformInformation
+): Promise<{ packagePath: string; serverPlatform: string }> {
     const roslynVersion = packageJSON.defaults.roslyn;
 
     // Find the matching server RID for the current platform.
@@ -93,22 +128,7 @@ async function installRoslyn(packageJSON: any, platformInfo?: PlatformInformatio
         `Microsoft.CodeAnalysis.LanguageServer.${serverPlatform}`,
         roslynVersion
     );
-
-    // Get the directory containing the server executable for the current platform.
-    const serverExecutableDirectory = path.join(packagePath, 'content', 'LanguageServer', serverPlatform);
-    if (!fs.existsSync(serverExecutableDirectory)) {
-        throw new Error(`Failed to find server executable directory at ${serverExecutableDirectory}`);
-    }
-
-    console.log(`Extracting Roslyn executables from ${serverExecutableDirectory}`);
-
-    // Copy the files to the language server directory.
-    fs.mkdirSync(languageServerDirectory);
-    fsextra.copySync(serverExecutableDirectory, languageServerDirectory);
-    const languageServerDll = path.join(languageServerDirectory, 'Microsoft.CodeAnalysis.LanguageServer.dll');
-    if (!fs.existsSync(languageServerDll)) {
-        throw new Error(`Failed to copy server executable`);
-    }
+    return { packagePath, serverPlatform };
 }
 
 async function installRazor(packageJSON: any, platformInfo: PlatformInformation) {