Format _apply_type_annotations.py in margin-oriented style

[stroxler]

In python code - and especially typed python code - I find it much easier to skim function headers if we always follow the style of

def f(
    x: SomeType
) -> ReturnType:
    ...

With this format I find it far easier to skim code because all the arg names are along the margin and the return types are in a predictable column. I don't usually change other folks' code to this style, but in the case of this module I'm the primary maintainer so I think it makes sense to go with what I find easier to maintain :)

(Someday I'm going to write a LibCST codemod that enforces this style!)

[codecov-commenter]

Codecov Report

Merging #600 (faf4b1d) into main (5f22b6c) will not change coverage.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##             main     #600   +/-   ##
=======================================
  Coverage   94.72%   94.72%           
=======================================
  Files         244      244           
  Lines       24916    24916           
=======================================
  Hits        23602    23602           
  Misses       1314     1314           

Impacted Files	Coverage Δ
libcst/codemod/visitors/_apply_type_annotations.py	94.17% <100.00%> (ø)

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[stroxler]

Closing this because it's going to clash with #596

I'm going to write a codemod that can do this automatically, and then run it on top of those changes after they merge :)