Create ClipboardManager from the main thread

The ClipboardManager is instantiated by the first call to
ServiceManager.getClipboardManager().

Now that scrcpy uses android.content.ClipboardManager directly, it must
ensure that it is created on the main thread (or at least on a thread
with a Looper), to avoid the following error:

> Can't create handler inside thread that has not called
> Looper.prepare()

Refs 8a02e3c2f58cffc3fdd8c08b26aae04bbf9d5a97
Fixes #6151 <https://github.com/Genymobile/scrcpy/issues/6151>