Add tests for multiline callable struct signatures

[fredrikekre]

Regression tests for #153: a function signature with newlines inside the
callee parentheses parses as an anonymous function with a tuple body
instead of as a call, so the formatter split the )( and broke the
code. Fixed upstream in JuliaSyntax#580.

Closes #153.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 46.36%. Comparing base (86c76e2) to head (8758cff).
⚠️ Report is 2 commits behind head on master.

❗ There is a different number of reports uploaded between BASE (86c76e2) and HEAD (8758cff). Click for more details.

HEAD has 5 uploads less than BASE

Flag	BASE (86c76e2)	HEAD (8758cff)
	8	3

Additional details and impacted files

@@             Coverage Diff             @@
##           master     #216       +/-   ##
===========================================
- Coverage   90.58%   46.36%   -44.23%     
===========================================
  Files           9        8        -1     
  Lines        4080     4130       +50     
===========================================
- Hits         3696     1915     -1781     
- Misses        384     2215     +1831     

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