Refactor code handling interface default methods to work on JDK 16+ ..

[leonard84]

see individual commits

[codecov]

Codecov Report

Merging #1407 (8776356) into master (3fa80ca) will decrease coverage by 0.02%.
The diff coverage is 82.60%.

@@             Coverage Diff              @@
##             master    #1407      +/-   ##
============================================
- Coverage     79.46%   79.44%   -0.03%     
  Complexity     3992     3992              
============================================
  Files           403      403              
  Lines         12537    12537              
  Branches       1642     1640       -2     
============================================
- Hits           9963     9960       -3     
- Misses         1978     1980       +2     
- Partials        596      597       +1     

Impacted Files	Coverage Δ
.../spockframework/mock/runtime/CglibMockFactory.java	0.00% <0.00%> (ø)
...va/org/spockframework/runtime/ExtensionRunner.java	100.00% <ø> (ø)
...untime/extension/builtin/ConditionalExtension.java	81.69% <ø> (ø)
...runtime/extension/builtin/PreconditionContext.java	90.32% <ø> (ø)
...ockframework/util/AbstractExpressionConverter.java	31.37% <ø> (ø)
...src/main/java/org/spockframework/util/MopUtil.java	24.56% <ø> (ø)
...n/java/org/spockframework/util/ReflectionUtil.java	80.00% <ø> (-0.36%)	⬇️
...in/java/org/spockframework/lang/SpecInternals.java	68.35% <72.00%> (ø)
...ckframework/mock/runtime/DefaultMethodInvoker.java	80.00% <75.00%> (-10.48%)	⬇️
...main/java/org/spockframework/compiler/AstUtil.java	80.28% <100.00%> (ø)
... and 18 more

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 3fa80ca...8776356. Read the comment docs.

[kriegaex]

How about renaming this PR into "Refactor code handling interface default methods to work on JDK 16+" or so? I know, you also removed pre-Java-8 cruft, but when later maybe referencing the PR in release notes or so, it might help if it has a more catchy name. 🙂