Log the current Swift extension version on activation (#1813)

I noticed we don't actually print the current extension version anywhere
in the logs, making the Capture Diagnostics command less useful.

Print the version of the extension the user is running in the log line
printed during extension activation.

Author: plemarquand

src/extension.ts

@@ -61,7 +61,9 @@ export async function activate(context: vscode.ExtensionContext): Promise<Api> {
             "swift-vscode-extension.log"
         );
         context.subscriptions.push(logger);
-        logger.info("Activating Swift for Visual Studio Code...");
+        logger.info(
+            `Activating Swift for Visual Studio Code ${context.extension.packageJSON.version}...`
+        );
 
         checkAndWarnAboutWindowsSymlinks(logger);