[Python-ideas] add !p to pprint.pformat() in str.format() an f-strings

Right now in str.format(), we have !s, !r, and !a to allow us to call str(), repr(), and ascii() respectively on the given expression. I'm proposing that we add a !p conversion to have pprint.pformat() be called to convert the given expression to a 'pretty' string. Calling ``` print(f"My dict: {d!p}") ``` is a lot more concise than: ``` import pprint print(f"My dict: {pprint.pformat(d)}") ``` We may even be able to have a static attribute stored to change the various default kwargs of pprint.pformat().