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

[Per Minborg]

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">

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Commit messages:
 - Clean up
 - Optimize str_len variants
 - Optimize strlen_short
 - Fix allocation size
 - Fix test with strcat

Changes: https://git.openjdk.org/panama-foreign/pull/862/files
 Webrev: https://webrevs.openjdk.org/?repo=panama-foreign&pr=862&range=00
  Stats: 700 lines in 4 files changed: 597 ins; 48 del; 55 mod
  Patch: https://git.openjdk.org/panama-foreign/pull/862.diff
  Fetch: git fetch https://git.openjdk.org/panama-foreign.git pull/862/head:pull/862

PR: https://git.openjdk.org/panama-foreign/pull/862