Extract functionality to download GitHub database

This was nested in a method that included prompting the user for a
github repo.

We'd like to re-use this to download a database of our choice from
GitHub, based on which language a user chooses.

extensions/ql-vscode/src/databaseFetcher.ts

@@ -78,6 +78,10 @@ export async function promptImportInternetDatabase(
  *
  * @param databaseManager the DatabaseManager
  * @param storagePath where to store the unzipped database.
+ * @param credentials the credentials to use to authenticate with GitHub
+ * @param progress the progress callback
+ * @param token the cancellation token
+ * @param cli the CodeQL CLI server
  */
 export async function promptImportGithubDatabase(
   commandManager: AppCommandManager,
@@ -103,6 +107,47 @@ export async function promptImportGithubDatabase(
     return;
   }
 
+  const databaseItem = await downloadGitHubDatabase(
+    githubRepo,
+    databaseManager,
+    storagePath,
+    credentials,
+    progress,
+    token,
+    cli,
+  );
+
+  if (databaseItem) {
+    await commandManager.execute("codeQLDatabases.focus");
+    void showAndLogInformationMessage(
+      "Database downloaded and imported successfully.",
+    );
+    return databaseItem;
+  }
+
+  return;
+}
+
+/**
+ * Downloads a database from GitHub
+ *
+ * @param githubRepo the GitHub repository to download the database from
+ * @param databaseManager the DatabaseManager
+ * @param storagePath where to store the unzipped database.
+ * @param credentials the credentials to use to authenticate with GitHub
+ * @param progress the progress callback
+ * @param token the cancellation token
+ * @param cli the CodeQL CLI server
+ **/
+export async function downloadGitHubDatabase(
+  githubRepo: string,
+  databaseManager: DatabaseManager,
+  storagePath: string,
+  credentials: Credentials | undefined,
+  progress: ProgressCallback,
+  token: CancellationToken,
+  cli?: CodeQLCliServer,
+): Promise<DatabaseItem | undefined> {
   const nwo = getNwoFromGitHubUrl(githubRepo) || githubRepo;
   if (!isValidGitHubNwo(nwo)) {
     throw new Error(`Invalid GitHub repository: ${githubRepo}`);
@@ -130,7 +175,7 @@ export async function promptImportGithubDatabase(
    * We only need the actual token string.
    */
   const octokitToken = ((await octokit.auth()) as { token: string })?.token;
-  const item = await databaseArchiveFetcher(
+  return await databaseArchiveFetcher(
     databaseUrl,
     {
       Accept: "application/zip",
@@ -143,14 +188,6 @@ export async function promptImportGithubDatabase(
     token,
     cli,
   );
-  if (item) {
-    await commandManager.execute("codeQLDatabases.focus");
-    void showAndLogInformationMessage(
-      "Database downloaded and imported successfully.",
-    );
-    return item;
-  }
-  return;
 }
 
 /**