[foreign-memaccess+abi] RFR: Improve strlen performance

[Per Minborg]

On Mon, 14 Aug 2023 09:52:10 GMT, Per Minborg <pminborg at openjdk.org> wrote:

> This PR suggests removing the use of native calls for strlen and instead use Java implementations.
> 
> The PR also suggest performance improvements for quad word strlen.
> 
> Here are some benchmarks that compares the performance of the new proposed methods with the performance of the JDK 21 variants (called "legacy" methods):
> 
> <img width="2596" alt="image" src="https://github.com/openjdk/panama-foreign/assets/7457876/c785f341-c826-4e3e-bf56-8387b1e96010">

In the benchmark `InternalStrLen.java` it would be better to `--add-exports=java.base/jdk.internal.foreign=ALL-UNNAMED` and run the real methods. For some reason, that does not work so suggestions are welcome on how to fix that.

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PR Comment: https://git.openjdk.org/panama-foreign/pull/862#issuecomment-1677031436