RFR: 8245094: Reduce overhead of initializing the default StringConcatFactory strategy

[Claes Redestad]

Hi,

by adding a bridge method in JavaLangAcces to call into the
StringConcatHelper.initialCoder - which is done only once during
initialization - we can reduce bootstrap overhead of SCF by a few
million instructions - ~0.5ms on wall clock measures.

Webrev: http://cr.openjdk.java.net/~redestad/8245094/open.00/
Bug:    https://bugs.openjdk.java.net/browse/JDK-8245094

Testing: tier1

Thanks!

/Claes