Only allow valid return types for willReturn

[MichelHartmann]

Another enhancement from the code sprint at @flyeralarm in Würzburg:

This fixes: #3122 and #3602

If you would like me to change something before it can merged just give me a hint.

[codecov]

Codecov Report

Merging #3673 into master will increase coverage by 0.22%.
The diff coverage is 96.46%.

@@             Coverage Diff             @@
##             master   #3673      +/-   ##
===========================================
+ Coverage     83.08%   83.3%   +0.22%     
- Complexity     3716    3802      +86     
===========================================
  Files           143     154      +11     
  Lines          9779    9940     +161     
===========================================
+ Hits           8125    8281     +156     
- Misses         1654    1659       +5

Impacted Files	Coverage Δ	Complexity Δ
src/Framework/MockObject/NullType.php	100% <100%> (ø)	3 <3> (?)
src/Framework/MockObject/InvocationMocker.php	76.27% <100%> (ø)	24 <0> (ø)	⬇️
src/Framework/MockObject/ConfigurableMethods.php	100% <100%> (ø)	2 <2> (?)
src/Framework/MockObject/TypeName.php	100% <100%> (ø)	12 <12> (?)
src/Framework/MockObject/MockMethod.php	89.82% <100%> (+2.76%)	50 <8> (-1)	⬇️
src/Framework/MockObject/Type.php	100% <100%> (ø)	18 <18> (?)
src/Framework/MockObject/MockClass.php	100% <100%> (ø)	4 <4> (?)
src/Framework/MockObject/Generator.php	75.78% <100%> (-0.5%)	143 <61> (-1)
.../Framework/MockObject/Builder/InvocationMocker.php	85.56% <100%> (+4.74%)	33 <10> (+9)	⬆️
src/Framework/MockObject/ObjectType.php	100% <100%> (ø)	10 <10> (?)
... and 20 more

---

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[psalm-shepherd]

Psalm didn’t find any errors!

[sebastianbergmann]

Thank you, @MichelHartmann. This is a lot to review, I hope I'll get to it soon.

[sebastianbergmann]

@MichelHartmann Sorry that it took so long to merge this. Thanks again!