Panels create actions that are disposed of on startup

From #162902 On startup, I noticed that we end up disposing of panel actions: https://github.com/microsoft/vscode/blob/36fdf6b697cba431beb6e391b5a8c5f3606975a1/src/vs/workbench/browser/parts/activitybar/activitybarPart.ts#L787 This is not great because we just created these actions and they have never been shown to the user. Since we then immediately dispose of them, it would be better to have simply skipped all this work. Here's an example call stack of where the actions are disposed on startup:  To improve startup performance, I suggest: - Start by seeing if we can defer creating the actions until they are visible - Seeing if we can defer doing even more work for composites that are not visible