RFR: 8338930: StringConcatFactory hardCoded string concatenation strategy [v3]

[Shaojin Wen]

> This is a follow-up to PR #20273, which improves performance when the number of parameters exceeds 20.
> 
> When the number of parameters is large, the possibility of reuse will be lower, so we can use the static concat method and write the length and coder directly into the bytecode to solve the performance regression problem.

Shaojin Wen has updated the pull request incrementally with one additional commit since the last revision:

  add control flag `reuseThreshold`

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Changes:
  - all: https://git.openjdk.org/jdk/pull/20675/files
  - new: https://git.openjdk.org/jdk/pull/20675/files/a016723f..432db40e

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=20675&range=02
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=20675&range=01-02

  Stats: 6 lines in 1 file changed: 4 ins; 0 del; 2 mod
  Patch: https://git.openjdk.org/jdk/pull/20675.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/20675/head:pull/20675

PR: https://git.openjdk.org/jdk/pull/20675