The pprint() code has a number of type or protocol specific handlers but doesn't have one for dict views.  So, we don't get pretty printing for the key(), values(), and items():

d = {i:i for i in range(100)}
pprint(d)             # This is handled correctly
pprint(d.keys())      # Printed on one line
pprint(d.values())    # Printed on one line
pprint(d.items())     # Printed on one line

According to the documentation for pprint, it is supposed to print objects on a single line if possible. See the second paragraph here: https://docs.python.org/3/library/pprint.html

More accurate to say that it aspires to print in a single line ONLY if the content fits in the specified width.  Otherwise, it prints vertically with appropriate indentation.  Indeed, that is the entire purpose of the module; otherwise, we would just use print() which always writes one line.

I have tried to add this. The PR adds:
- PrettyPrinter._pprint_dict_view to handle dict_keys and dict_values (sorted with _safe_key).
= PrettyPrinter._pprint_dict_items_view to handle dict_items (sorted using _safe_tuple).
- Tests.

Would a NEWS entry or other form of documentation be necessary?

The PR looks good!  When the last comments are resolved, unless there is activity from other core devs, I will merge it.