src/goModules.ts: open go.mod after init

Running go mod init creates a new go.mod file in the workspace
folder. However it is currently unclear that the operation ran
or succeeded. This change logs messages to the output channel
and opens the go.mod file when the command has succeeded.

Change-Id: Ie384356612a3da58edbf3d8c7525f6d66084486d
Reviewed-on: https://go-review.googlesource.com/c/vscode-go/+/322929
Trust: Suzy Mueller <suzmue@golang.org>
Run-TryBot: Suzy Mueller <suzmue@golang.org>
TryBot-Result: kokoro <noreply+kokoro@google.com>
Reviewed-by: Hyang-Ah Hana Kim <hyangah@gmail.com>

Author: suzmue

src/goModules.ts

@@ -200,10 +200,15 @@ export async function goModInit() {
 	try {
 		const env = toolExecutionEnvironment();
 		const cwd = getWorkspaceFolderPath();
+		outputChannel.appendLine(`Running "${goRuntimePath} mod init ${moduleName}"`);
 		await execFile(goRuntimePath, ['mod', 'init', moduleName], { env, cwd });
+		outputChannel.appendLine('Module successfully initialized. You are ready to Go :)');
+		vscode.commands.executeCommand('vscode.open', vscode.Uri.file(path.join(cwd, 'go.mod')));
 	} catch (e) {
 		outputChannel.appendLine(e);
 		outputChannel.show();
-		vscode.window.showErrorMessage(`Error running 'go mod init ${moduleName}': See Go output channel for details`);
+		vscode.window.showErrorMessage(
+			`Error running "${goRuntimePath} mod init ${moduleName}": See Go output channel for details`
+		);
 	}
 }