RFR: 8171855: Move package name transformations during module bootstrap into VM

[Claes Redestad]

Hi,

during jigsaw bootstrap, package names - represented in external form,
"java.lang" - are transformed into VM internal form, "java/lang",
before calling into the VM.

This, however, can effectively be moved into the VM, which removes the
need to generate a lot of short-lived strings during bootstrap and heat
up various String.replace-related methods.  This has a noticeable impact
on startup metrics.

Webrev: http://cr.openjdk.java.net/~redestad/8171855/
Bug: https://bugs.openjdk.java.net/browse/JDK-8171855

JPRT -testset hotspot pass, and I've prepared to push this into jdk9/hs
if there are no objections.

Char-based replace on a UTF-8 source should be correct as long as the
from and to chars are ASCII (0x00 through 0x7F).  A more general method
would be needed to safely deal with char values above 0x7F, so adding
some asserts to that effect should be considered.

Thanks!

/Claes