Compile Test Snippets on Java 14

[cortinico]

As discussed in #2797, let's move compile-test-snippets to Java 14.
I've adapted the tests to have a green build 👍

[codecov]

Codecov Report

Merging #2803 into master will not change coverage.
The diff coverage is n/a.

@@            Coverage Diff            @@
##             master    #2803   +/-   ##
=========================================
  Coverage     80.52%   80.52%           
  Complexity     2323     2323           
=========================================
  Files           386      386           
  Lines          6957     6957           
  Branches       1262     1262           
=========================================
  Hits           5602     5602           
  Misses          726      726           
  Partials        629      629           

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[arturbosch]

As discussed in #2797, let's move compile-test-snippets to Java 14.
I've adapted the tests to have a green build

Thanks for using the housekeeping label :).