RFR: 8301958: Avoid Arrays.copyOfRange overhead in java.lang.String [v3]

[Claes Redestad]

> This adds a local, specialized `copyBytes` method to `String` that avoids certain redundant range checks and clamping that JIT has issues removing fully.
> 
> This has a small but statistically significant effect on `String` microbenchmarks, eg.:
> 
> Baseline
> 
> Benchmark                                            (size)  Mode  Cnt   Score   Error  Units
> StringConstructor.newStringFromArray                      7  avgt   15  16.817 ± 0.369  ns/op
> StringConstructor.newStringFromArrayWithCharset           7  avgt   15  16.866 ± 0.449  ns/op
> StringConstructor.newStringFromArrayWithCharsetName       7  avgt   15  22.198 ± 0.396  ns/op
> 
> 
> Patch:
> 
> Benchmark                                            (size)  Mode  Cnt   Score   Error  Units
> StringConstructor.newStringFromArray                      7  avgt   15  15.477 ± 0.342  ns/op
> StringConstructor.newStringFromArrayWithCharset           7  avgt   15  15.557 ± 0.352  ns/op
> StringConstructor.newStringFromArrayWithCharsetName       7  avgt   15  21.272 ± 0.398  ns/op
> 
> 
> Care has to be taken to ensure preconditions have been checked when using `checkBytes`. In the case of `String(AbstractStringBuilder)` there's a possible pre-existing issue where the constructor might either throw an exception or truncate the buffer if the builder byte array and length is not in agreement (theoretically possible if you clear/remove and call `trimToSize()` concurrently). Adding an explicit check here seem to be the right thing to do regardless of this RFE.

Claes Redestad has updated the pull request incrementally with one additional commit since the last revision:

  Update StringLatin1.trim for consistency

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/12453/files
  - new: https://git.openjdk.org/jdk/pull/12453/files/5b637e09..a5e494bc

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=12453&range=02
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=12453&range=01-02

  Stats: 9 lines in 2 files changed: 0 ins; 0 del; 9 mod
  Patch: https://git.openjdk.org/jdk/pull/12453.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/12453/head:pull/12453

PR: https://git.openjdk.org/jdk/pull/12453