Please review JDK-8035312

[Marcus Lagergren]

Please review 

https://bugs.openjdk.java.net/browse/JDK-8035312 <https://bugs.openjdk.java.net/browse/JDK-8035312>

There were several corner cases related to length in general and setting length in arrays to not writable in particular. 
None of the existing run times pass all the tests, so this was a very hard area to get right (added 6 new unit tests)

I’ve also gotten rid of the special casey length not writable SwitchPoint in NativeArray - now that I have a filter for LengtNotWritableArray that can’t be cast to a ContinuousArrayData in the fast paths, this handles itself anyway.

webrev at: http://cr.openjdk.java.net/~lagergren/8035312/

/M