RFR: 8339874: Avoid duplicate checking of trailing slash in ZipFile.getZipEntry

[Eirik Bjørsnøs]

Please review this PR which speeds up `ZipFile.getZipEntry` by removing slash-checking logic which is already taking place during lookup in `ZipFile.Source.getEntryPos`. 

`ZipFile.Source.getEntryPos` includes logic to match a lookup for "name" against a directory entry "name/" (with a trailing slash). However, only the CEN position is currently returned, so `ZipFile.getZipEntry` needs to re-read the name from the CEN and determine if a trailing slash needs to be appended to the name of the returned `ZipEntry`.

By letting `ZipFile.Source.getEntryPos` return the resolved name along with the CEN position (in a new record `EntryPos`), `ZipFile.getZipEntry` can now instead use the already resolved name. 

This results in a nice ~18% speedup in the `ZipFileGetEntry.getEntryHit` micro:

Baseline:


Benchmark                    (size)  Mode  Cnt   Score   Error  Units
ZipFileGetEntry.getEntryHit     512  avgt   15  63.713 ? 2.645  ns/op
ZipFileGetEntry.getEntryHit    1024  avgt   15  67.405 ? 1.474  ns/op


PR:


Benchmark                    (size)  Mode  Cnt   Score   Error  Units
ZipFileGetEntry.getEntryHit     512  avgt   15  52.027 ? 2.669  ns/op
ZipFileGetEntry.getEntryHit    1024  avgt   15  55.211 ? 1.169  ns/op


This purely a cleanup and optimization PR, no functional tests are changed or added.

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Commit messages:
 - Avoid repeated checking of trailing slash in ZipFile.getZipEntry

Changes: https://git.openjdk.org/jdk/pull/20939/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=20939&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8339874
  Stats: 59 lines in 2 files changed: 17 ins; 21 del; 21 mod
  Patch: https://git.openjdk.org/jdk/pull/20939.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/20939/head:pull/20939

PR: https://git.openjdk.org/jdk/pull/20939