Insert two empty lines after top level suite with trailing def/class

[konstin]

Black formats

if True:

    def double(s):
        return s + s
print("out")

as

if True:

    def double(s):
        return s + s


print("out")

while we format it as

if True:

    def double(s):
        return s + s

print("out")

Black does so because on the top level, there are two newlines after a function or class definition. We currently don't see that the if statement is on the top level when formatting its suite, so we can't that we need one more newline here. This is a follow-up to #7946.

[konstin]

Works on main