RFR: 8261154: Memory leak in Java_java_lang_ClassLoader_defineClass0 with long class names

[Claes Redestad]

This patch resolves a potential memory leak in Java_java_lang_ClassLoader_defineClass0

I've not figured a good way to write a regression test, but manually verified the leak and the fix by adding a microbenchmark that triggers the leak. When run with `-XX:NativeMemoryTracking=summary -XX:+UnlockDiagnosticVMOptions -XX:+PrintNMTStatistics` there will be a section of memory of unknown origin, e.g.:

-                   Unknown (reserved=65536KB, committed=55104KB)
                            (mmap: reserved=65536KB, committed=55104KB) 

With the patch, there is no memory unaccounted for.

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Commit messages:
 - Add code used to generate the X_LONG_NAME_BYTECODE
 - Add micros showcasing leak
 - Resolve memory leak in defineClass0

Changes: https://git.openjdk.java.net/jdk/pull/2407/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=2407&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8261154
  Stats: 88 lines in 2 files changed: 84 ins; 0 del; 4 mod
  Patch: https://git.openjdk.java.net/jdk/pull/2407.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/2407/head:pull/2407

PR: https://git.openjdk.java.net/jdk/pull/2407