Improve sdkmanager fetching for package data

Due to the slowness of running `sdkmanager --list` command, the Android Settings page, the New Android Device wizard, are quite slow, taking more than 4 seconds to finish.

One option to mitigate this is by running `sdkmanager --list_installed` when it makes sense, that is whenever we're trying to list data only and there's no intention to install new packages, this would apply to the New Android Device wizard, and some cases in the Settings page.

Another option is caching the content of `sdkmanager --list` and using the cached content to parse the data for all cases except when we want to install new SDK or when running the SDK Manager Dialog. Also, the Android SDK directory could be watched for changes to refresh this cache in case packages are modified outside of Qt Creator.