Support 3.12 feature: PEP 701 – Syntactic formalization of f-strings

The following valid Python samples from https://peps.python.org/pep-0701/ running under 3.12.0rc1 will cause exceptions in YAPF.

bag = {'wand': 'Elder'}
print(f'Magic wand: { bag['wand'] }')

source = 'a_file.py'
print(f"{source.removesuffix(".py")}.c: $(srcdir)/{source}")

print(f"{f"{f"{f"{f"{f"{1+1}"}"}"}"}"}")

x = 1
y = 2
print(
    f"___{
        x
    }___"
)
print(
    f"___{(
        y
    )}___"
)

my_dict = {"key": "value"}
print(f" something { my_dict["key"] } something else ")

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