RFR: 8175891, 8192892: JrtPath improvements

[Claes Redestad]

Hi,

please review this patch that resolves two small but sometimes 
significant inefficiencies in jdk.internal.jrtfs.JrtPath:

Improve JrtPath::getResolved fast-path test:
https://bugs.openjdk.java.net/browse/JDK-8192892

Testing for '.' is insufficient as it's likely all paths have a dot in 
them, while resolving is rare. Patch uses a test that is logically 
equivalent to that in ZipPath::getResolved to better filter out paths 
that don't need to take the slow path.

JrtPath::resolve off-by-one pre-sizing cause for memory pressure:
https://bugs.openjdk.java.net/browse/JDK-8175891

As path is normalized to never end with a / this code can be simplified.

Webrev: http://cr.openjdk.java.net/~redestad/8192892/open.0/

In a JMH micro[1] that naively walks all entries in the JDK lib/modules 
and counts classes, these fixes work together to remove overhead both in 
repeated and single-shot settings (the latter is relevant since jrtfs 
usage may influence startup times in certain applications and tools):

Benchmark           Mode  Cnt  Score   Error  Units
JRTWalk.walkJImage  avgt   25  0.049 ± 0.003   s/op
JRTWalk.walkJImage  avgt   25  0.027 ± 0.001   s/op  # 1.8x

Benchmark           Mode  Cnt  Score   Error  Units
JRTWalk.walkJImage    ss   20  0.436 ± 0.018   s/op  (best: 0.389 s/op)
JRTWalk.walkJImage    ss   20  0.388 ± 0.017   s/op  (best: 0.363 s/op)

Thanks!

/Claes

[1] http://cr.openjdk.java.net/~redestad/8192892/JRTWalk.java