RFR: 8342806: Desugar capturing lambda in StringNameTable

[Claes Redestad]

- Desugar `computeIfAbsent` to `get` & `put` to avoid a capturing lambda. Since the map is a non-synchronized `HashMap` this is just as non-thread-safe as before.
- Salvage the microbenchmark added as a JBS comment to https://bugs.openjdk.org/browse/JDK-8268622 
- Microbenchmark show a modest reduction in allocations for tests stressing `StringNameTable` (Macbook M1):


Name                  Cnt         Base         Error          Test         Error   Unit  Change
testInternStringTable  10       55,731 ±       3,701        51,083 ±       2,062  ms/op   1,09x (p = 0,000*)
  :gc.alloc.rate.norm     54705366,956 ±  375197,844  53936224,624 ± 1421298,600   B/op   0,99x (p = 0,031 )
testSharedTable        10       47,997 ±       5,802        48,022 ±       4,968  ms/op   1,00x (p = 0,988 )
  :gc.alloc.rate.norm     56562680,368 ± 1535117,433  53403645,438 ±  218526,779   B/op   0,94x (p = 0,000*)
testStringTable        10       45,933 ±       2,542        44,094 ±       1,360  ms/op   1,04x (p = 0,009*)
  :gc.alloc.rate.norm     56244541,359 ± 1019940,919  53226602,956 ±  510018,314   B/op   0,95x (p = 0,000*)
testUnsharedTable      10       60,474 ±       1,912        59,068 ±       1,038  ms/op   1,02x (p = 0,008*)
  :gc.alloc.rate.norm     66970079,820 ± 1402704,512  67285851,746 ±  883540,307   B/op   1,00x (p = 0,377 )
  * = significant

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Commit messages:
 - copyright
 - Add internStringTable micro
 - More micro tuning
 - Tune micro
 - Fully desugar
 - Add micro
 - Allocating capturing lambda in StringNameTable

Changes: https://git.openjdk.org/jdk/pull/21631/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=21631&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8342806
  Stats: 152 lines in 2 files changed: 150 ins; 0 del; 2 mod
  Patch: https://git.openjdk.org/jdk/pull/21631.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/21631/head:pull/21631

PR: https://git.openjdk.org/jdk/pull/21631