Add Cyclomatic Complexity implementation for Java

[marco-ballario]

This PR adds the Cyclomatic Complexity metrics implementation for the Java language. Two unit tests are added to verify the correct computation of the measures. Thanks in advance for the review.

[marco-c]

CC @dburriss, since he's interested in Java support

[codecov-commenter]

Codecov Report

Merging #786 (0722e37) into master (e378b60) will decrease coverage by 0.06%.
The diff coverage is 88.23%.

@@            Coverage Diff             @@
##           master     #786      +/-   ##
==========================================
- Coverage   39.76%   39.69%   -0.07%     
==========================================
  Files          51       51              
  Lines        6810     6827      +17     
  Branches      972      975       +3     
==========================================
+ Hits         2708     2710       +2     
- Misses       3446     3453       +7     
- Partials      656      664       +8     

Impacted Files	Coverage Δ
src/metrics/cyclomatic.rs	77.02% <88.23%> (+1.45%)	⬆️
src/node.rs	71.15% <0.00%> (-15.39%)	⬇️
src/getter.rs	76.52% <0.00%> (-2.61%)	⬇️
src/spaces.rs	74.39% <0.00%> (-1.22%)	⬇️
src/metrics/nargs.rs	74.41% <0.00%> (-0.39%)	⬇️
src/metrics/loc.rs	80.28% <0.00%> (+0.24%)	⬆️
src/metrics/cognitive.rs	72.07% <0.00%> (+0.32%)	⬆️
src/metrics/halstead.rs	72.98% <0.00%> (+0.57%)	⬆️
src/metrics/exit.rs	74.77% <0.00%> (+0.90%)	⬆️

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[dburriss]

Nice good to see.

[calixteman]

LGTM. Thank you.

[calixteman]

Unrelated to this change, but in looking to the code for js, I think we (I ??) missed to add operators like ?? and ?. (maybe others ?): they're lazy evaluated like a || or a &&.
Oh and probably ||=, &&= are missing too.

[Luni-4]

Yep, right, we forgot them. Could you please open an issue in order to remember them? Thank you @calixteman! :)