RFR: 8317837: Leftover FFM implementation-only changes

[Jorn Vernee]

Port of miscellaneous leftover implementation-only changes from the panama-foreign repo:

These four related to improving the performance of the internal `strlen` implementation:

  - https://github.com/openjdk/panama-foreign/pull/862
  - https://github.com/openjdk/panama-foreign/pull/860
  - https://github.com/openjdk/panama-foreign/pull/858
  - https://github.com/openjdk/panama-foreign/pull/857
  
Adding new benchmarks:
  
  - https://github.com/openjdk/panama-foreign/pull/874
  - https://github.com/openjdk/panama-foreign/pull/870

Other misc. changes:

  - https://github.com/openjdk/panama-foreign/pull/885
  - https://github.com/openjdk/panama-foreign/pull/886
  - https://github.com/openjdk/panama-foreign/pull/864
  - https://github.com/openjdk/panama-foreign/pull/903
  - https://github.com/openjdk/panama-foreign/pull/890 (note that this is a javadoc block in the implementation only)
  - https://github.com/openjdk/panama-foreign/pull/908
  - https://github.com/openjdk/panama-foreign/pull/910

-------------

Commit messages:
 - Do not run a lengthy test on zero machines
 - 8317137: Time out in TestStringEncoding
 - adjust misformatted copyright header
 - Fix arithmetic bug in SegmentAllocator
 - Improve exception messages and simplify LayoutPath
 - 8316196: Use hexadecimal form for address outputs in java.lang.foreign
 - Benchmark Java to/from C string conversions
 - Add AllocTest benchmark
 - Avoid using StandardCharset in Java code
 - Improve strlen performance
 - ... and 4 more: https://git.openjdk.org/jdk/compare/32ac72c3...b60dbff1

Changes: https://git.openjdk.org/jdk/pull/16128/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=16128&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8317837
  Stats: 1358 lines in 19 files changed: 1261 ins; 11 del; 86 mod
  Patch: https://git.openjdk.org/jdk/pull/16128.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/16128/head:pull/16128

PR: https://git.openjdk.org/jdk/pull/16128