RFR: 8245969: Simplify String concat constant folding

[Claes Redestad]

Hi,

please review this patch to StringConcatFactory which (I think)
simplifies the folding of constants around arguments by folding any
suffix constant into the newArray combinator instead.

This simplifies the code in all prependers and in the general flow of
the bootstrap code, at the cost of some added complexity around newArray
and the new newArrayPrepend combinator. Slightly improves bootstrap and
footprint overheads by not having to bind as many arguments to the
prependers.

Bug:    https://bugs.openjdk.java.net/browse/JDK-8245969
Webrev: http://cr.openjdk.java.net/~redestad/8245969/open.00

Testing: tier1+2

Thanks!

/Claes