RFR: 8261847: performace of java.lang.Record::toString should be improved

[Vicente Romero]

Please review this PR which aims to optimize the implementation of the `toString` method we provide for records. A benchmark comparing the implementation we are providing for records with lombok found out that lombok is much faster mainly because our implementation uses `String::format`. This fix is basically delegating on StringConcatFactory::makeConcatWithConstants which is faster.

TIA

This is the result of the benchmark comparing records to lombok with vanilla JDK:

Benchmark                          Mode  Cnt    Score    Error  Units
MyBenchmark.base                   avgt    4    0.849 ±  0.111  ns/op
MyBenchmark.equals_record          avgt    4    7.343 ±  2.740  ns/op
MyBenchmark.equals_value           avgt    4    6.644 ±  1.920  ns/op
MyBenchmark.record_hash_code       avgt    4    5.763 ±  3.882  ns/op
MyBenchmark.record_to_string       avgt    4  262.626 ± 12.574  ns/op               <------ Before
MyBenchmark.value_class_to_string  avgt    4   30.325 ± 21.389  ns/op
MyBenchmark.value_hash_code        avgt    4    5.048 ±  3.936  ns/op


after this patch:

Benchmark                          Mode  Cnt   Score   Error  Units
MyBenchmark.base                   avgt    4   0.680 ± 0.185  ns/op
MyBenchmark.equals_record          avgt    4   5.599 ± 1.348  ns/op
MyBenchmark.equals_value           avgt    4   5.718 ± 4.633  ns/op
MyBenchmark.record_hash_code       avgt    4   4.628 ± 4.368  ns/op
MyBenchmark.record_to_string       avgt    4  26.791 ± 1.817  ns/op                 <------- After
MyBenchmark.value_class_to_string  avgt    4  35.473 ± 2.626  ns/op
MyBenchmark.value_hash_code        avgt    4   6.152 ± 5.101  ns/op

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

Commit messages:
 - 8261847: Suboptimal java.lang.record's methods generation

Changes: https://git.openjdk.java.net/jdk/pull/6403/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=6403&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8261847
  Stats: 56 lines in 1 file changed: 20 ins; 15 del; 21 mod
  Patch: https://git.openjdk.java.net/jdk/pull/6403.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/6403/head:pull/6403

PR: https://git.openjdk.java.net/jdk/pull/6403