[Core] Extract throwable collector

[mpkorstanje]

Try and clean up the logic around throwing/re-throwing exceptions at various
abstraction levels a bit

[codecov]

Codecov Report

Merging #2281 (4ae0393) into v7.x.x (ebbd4b9) will increase coverage by 0.02%.
The diff coverage is 83.49%.

❗ Current head 4ae0393 differs from pull request most recent head 625f7c2. Consider uploading reports for the commit 625f7c2 to get more accurate results

@@             Coverage Diff              @@
##             v7.x.x    #2281      +/-   ##
============================================
+ Coverage     83.31%   83.33%   +0.02%     
- Complexity     2298     2323      +25     
============================================
  Files           291      295       +4     
  Lines          8241     8299      +58     
  Branches        733      737       +4     
============================================
+ Hits           6866     6916      +50     
- Misses         1092     1098       +6     
- Partials        283      285       +2     

Impacted Files	Coverage Δ
...n/java/io/cucumber/core/resource/ClassLoaders.java	28.57% <0.00%> (-4.77%)	⬇️
.../cucumber/core/runtime/TestCaseResultObserver.java	45.23% <ø> (ø)
...cumber/core/exception/UnrecoverableExceptions.java	50.00% <50.00%> (ø)
...ber/core/runtime/RethrowingThrowableCollector.java	70.83% <70.83%> (ø)
...io/cucumber/core/runner/TestAbortedExceptions.java	86.66% <86.66%> (ø)
...va/io/cucumber/core/runner/ThrowableCollector.java	88.88% <88.88%> (ø)
.../src/main/java/io/cucumber/core/runner/Runner.java	90.99% <90.90%> (-0.28%)	⬇️
...rc/main/java/io/cucumber/core/runtime/Runtime.java	92.92% <92.30%> (+0.46%)	⬆️
...n/java/io/cucumber/core/plugin/TeamCityPlugin.java	87.87% <100.00%> (ø)
...rc/main/java/io/cucumber/core/runner/TestStep.java	100.00% <100.00%> (ø)
... and 6 more

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