SoundEffect: Create predefined sounds as examples

[microbit-carlos]

We'll like to have two or three predefined SoundEffects that users could use to investigate and modify.

These predefined SoundEffects should be immutable, like the predefined Images. To modify them a copy can be created:

my_copy = audio.SoundEffect.EXAMPLE_1.copy()
my_copy.duration = 2000
audio.play(my_copy)

Of course, they should have descriptive names, not EXAMPLE_n :)

[microbit-carlos]

We haven't had any request for this yet, and we can always add pre-made SoundEffects to the Python Editor sidebar. So we'll close this was "won't implement" for the meantime.