Ability to pass Pillow's `Exif` to save without calling `tobytes`

[bigcat88]

Describe why it is important and where it will be useful

im = Image.new("L", size=(1, 1))
exif = im.getexif()
exif[Base.ImageDescription.value] = "description"
buf = BytesIO()
im.save(buf, format="HEIF", exif=exif)  # <-- here 
print(Image.open(buf).getexif())

Describe your proposed solution

If passed object is Pillow's Exif then pillow-heif itself should call tobytes method.

Describe alternatives you've considered, if relevant

No response

Additional context

Pillow itself supports such thing...