Reduce false positives on comparing unrelated types

[Johnnei]

scala> BigDecimal(5) == 0
val res0: Boolean = false

scala> BigDecimal(0) == 0
val res1: Boolean = true

Scapegoat still seem to get the Literal instead of the boxed variants which I observed in bytecode after diagnosing a violation in my codebases. This special clause will handle these cases.

[codecov-commenter]

Codecov Report

Base: 87.11% // Head: 87.19% // Increases project coverage by +0.08% 🎉

Coverage data is based on head (970327b) compared to base (7407ec6).
Patch coverage: 100.00% of modified lines in pull request are covered.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #710      +/-   ##
==========================================
+ Coverage   87.11%   87.19%   +0.08%     
==========================================
  Files         141      141              
  Lines        1521     1523       +2     
  Branches      221      221              
==========================================
+ Hits         1325     1328       +3     
+ Misses        196      195       -1     

Impacted Files	Coverage Δ
...inspections/equality/ComparingUnrelatedTypes.scala	96.00% <100.00%> (+4.69%)	⬆️

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[saeltz]

Thanks for your contribution!