RFR: 8317837: Leftover FFM implementation-only changes [v2]

[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
>   
> Testing: `jdk_foreign`

Jorn Vernee has updated the pull request incrementally with one additional commit since the last revision:

  8315041: Optimize Java to C string conversion by avoiding double copy
  
  Reviewed-by: pminborg

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/16128/files
  - new: https://git.openjdk.org/jdk/pull/16128/files/b60dbff1..cfc31040

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=16128&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=16128&range=00-01

  Stats: 87 lines in 5 files changed: 72 ins; 5 del; 10 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