examples : use xcframework in whisper.objc example (#2882)

examples : use xcframework in whisper.objc example (#2882)

* examples : use xcframework in whisper.objc example

This commit updates the whisper.objc example to use the xcframework.

The motivation for this to be consistent with the swift example and to
also act as a reference for how to use the xcframework in an objc
project.

Resolves: https://github.com/ggerganov/whisper.cpp/issues/2881

* examples : setup audio session viewDidload

This commit adds the setup of the audio session in the viewDidload
method of the ViewController.m file. This is necessary to allow the app
to record audio.

The motivation for this is that without this it was not possible to
caputue audio from the microphone. It was possible to click on the
Capture button but nothing happened after that, and the button was not
marked red indicating that the button could be clicked again to stop
capturing. With this change it is possible to capture audio from the
microphone and get it transcribed.