iOS Audio: Always deactivate device before setting new preferred samplerate

This fixes a bug on iOS 17 running on a 9th gen iPad.

- Set JUCE_IOS_AUDIO_EXPLICIT_SAMPLERATES=44100,48000,88200,96000
- Start the DemoRunner.
- Add a breakpoint in AudioDeviceManager::audioDeviceAboutToStartInt().
- In the DemoRunner, change the sample rate to 96000.
- The breakpoint will fire. Observe the value of
  getCurrentBufferSizeSamples().
- Move the breakpoint to audioDeviceIOCallbackInt and continue
  execution.
- The breakpoint will fire. Observe the value of the numSamples
  parameter.

numSamples should always be no larger than the sample count reported in
audioDeviceAboutToStartInt().

Before this change, it was possible for getCurrentBufferSizeSamples() to
return a value smaller than the buffer size of subsequent process
callbacks.

Removing the availability checks and unconditionally
deactivating/reactivating the device seems to fix this issue, and the
correct buffer size is returned immediately when the device is
(re)started.

modules/juce_audio_devices/native/juce_Audio_ios.cpp

@@ -426,13 +426,11 @@ struct iOSAudioIODevice::Pimpl final : public AsyncUpdater
         // a call to setActive, so we also need to wait for the first audio callback.
         // This will be slow!
         // https://developer.apple.com/library/archive/qa/qa1631/_index.html
-        if (@available (ios 18, *))
-            setAudioSessionActive (false);
+        setAudioSessionActive (false);
 
         JUCE_NSERROR_CHECK ([session setPreferredIOBufferDuration: bufferDuration error: &error]);
 
-        if (@available (ios 18, *))
-            setAudioSessionActive (true);
+        setAudioSessionActive (true);
 
         return getBufferSize (currentSampleRate);
     }