Range#{last, lastElement, terminalElement, ...} are completely undocumented and most likely broken

[scabug]

scala>  (0 to Int.MaxValue).last
res34: Int = -2

scala>  (0 to Int.MaxValue).lastElement
res35: Int = -2

scala>  (0 to Int.MaxValue).terminalElement
res36: Int = -1

scala>  (0 to Int.MaxValue).numRangeElements
res37: Int = -1

This mess is caused by no documentation (especially not about how possibly invalid inputs are treated), unhandled numeric overflows and made worse by making these things public.

The only reason why we don't check our inputs immediately is to allow by to work. That means every other method needs to enforce our invariants.

I assume the methods above are not the only ones which don't do this.

[scabug]

Imported From: https://issues.scala-lang.org/browse/SI-6747?orig=1
Reporter: @soc

[scabug]

@soc said:
scala/scala#2645