RFR: 8212597: Optimize String concatenation setup when using primitive operands

[Claes Redestad]

Hi,

this patch optimizes setup of the default strategy for indified String 
concat to setup and use fewer intermediary MHs when some arguments are 
non-char primitives.

Webrev: http://cr.openjdk.java.net/~redestad/8212597/jdk.00/
Bug: https://bugs.openjdk.java.net/browse/JDK-8212597

I've cleaned up of the associated StringConcatHelper to remove the 
mixCoder methods no longer in use, along with a small adjustment to the 
HelloClasslist tool to exercise more concatenation shapes. With the fix 
to https://bugs.openjdk.java.net/browse/JDK-8212201 in place this build 
tool always emit the latest bytecode, which ensures ISC is exercised and 
part of the feedback loop. This makes sure that input to jlink is kept 
relevant and up-to-date, and by adding a number of common concatenation 
shapes we reduce the startup overhead in a few common cases.

Testing: ran all String tests locally, sanity JDK tier 1+2 testing on 
primary platforms

Thanks!

/Claes