8372353: API to compute the byte length of a String encoded in a given Charset

[cushon]

This implements an API to return the byte length of a String encoded in a given charset. See JDK-8372353 for background.

---

Benchmark                              (encoding)  (stringLength)   Mode  Cnt          Score           Error  Units
StringLoopJmhBenchmark.getBytes             ASCII              10  thrpt    5  391708261.769 ± 131738312.833  ops/s
StringLoopJmhBenchmark.getBytes             ASCII             100  thrpt    5  177933535.422 ±   3491403.886  ops/s
StringLoopJmhBenchmark.getBytes             ASCII            1000  thrpt    5   39398051.383 ±   4874329.102  ops/s
StringLoopJmhBenchmark.getBytes             ASCII          100000  thrpt    5     450580.669 ±     13486.822  ops/s
StringLoopJmhBenchmark.getBytes            LATIN1              10  thrpt    5   39335958.647 ±   3349851.059  ops/s
StringLoopJmhBenchmark.getBytes            LATIN1             100  thrpt    5   65291332.456 ±   1826481.963  ops/s
StringLoopJmhBenchmark.getBytes            LATIN1            1000  thrpt    5   11357128.475 ±    137592.840  ops/s
StringLoopJmhBenchmark.getBytes            LATIN1          100000  thrpt    5     191677.869 ±      5699.104  ops/s
StringLoopJmhBenchmark.getBytes             UTF16              10  thrpt    5  104280405.379 ±   1105232.322  ops/s
StringLoopJmhBenchmark.getBytes             UTF16             100  thrpt    5   38559775.983 ±   3969525.959  ops/s
StringLoopJmhBenchmark.getBytes             UTF16            1000  thrpt    5    4223120.998 ±     53702.563  ops/s
StringLoopJmhBenchmark.getBytes             UTF16          100000  thrpt    5      56930.445 ±      1575.178  ops/s
StringLoopJmhBenchmark.getBytesLength       ASCII              10  thrpt    5  943085644.673 ±  26102941.766  ops/s
StringLoopJmhBenchmark.getBytesLength       ASCII             100  thrpt    5  391311481.624 ±   6970035.394  ops/s
StringLoopJmhBenchmark.getBytesLength       ASCII            1000  thrpt    5   99419040.393 ±   3951945.216  ops/s
StringLoopJmhBenchmark.getBytesLength       ASCII          100000  thrpt    5    1212863.635 ±      7312.029  ops/s
StringLoopJmhBenchmark.getBytesLength      LATIN1              10  thrpt    5  359884500.225 ±  40809523.322  ops/s
StringLoopJmhBenchmark.getBytesLength      LATIN1             100  thrpt    5  211044735.337 ±   7958529.416  ops/s
StringLoopJmhBenchmark.getBytesLength      LATIN1            1000  thrpt    5   91412629.228 ±   8086023.381  ops/s
StringLoopJmhBenchmark.getBytesLength      LATIN1          100000  thrpt    5    1195691.147 ±     47782.242  ops/s
StringLoopJmhBenchmark.getBytesLength       UTF16              10  thrpt    5  333554560.613 ±   3708669.415  ops/s
StringLoopJmhBenchmark.getBytesLength       UTF16             100  thrpt    5   81021924.141 ±  12571553.763  ops/s
StringLoopJmhBenchmark.getBytesLength       UTF16            1000  thrpt    5   10046196.775 ±   1595086.940  ops/s
StringLoopJmhBenchmark.getBytesLength       UTF16          100000  thrpt    5      99587.224 ±     33212.377  ops/s
StringLoopJmhBenchmark.utf8LenByLoop        ASCII              10  thrpt    5  408274674.923 ±  35589889.027  ops/s
StringLoopJmhBenchmark.utf8LenByLoop        ASCII             100  thrpt    5   79203663.276 ±    350888.625  ops/s
StringLoopJmhBenchmark.utf8LenByLoop        ASCII            1000  thrpt    5    8369222.519 ±    552376.540  ops/s
StringLoopJmhBenchmark.utf8LenByLoop        ASCII          100000  thrpt    5      86842.588 ±     16740.263  ops/s
StringLoopJmhBenchmark.utf8LenByLoop       LATIN1              10  thrpt    5  364012818.025 ±  47011914.698  ops/s
StringLoopJmhBenchmark.utf8LenByLoop       LATIN1             100  thrpt    5   82681217.184 ±   9930544.695  ops/s
StringLoopJmhBenchmark.utf8LenByLoop       LATIN1            1000  thrpt    5   10040934.803 ±   1934154.553  ops/s
StringLoopJmhBenchmark.utf8LenByLoop       LATIN1          100000  thrpt    5      88037.251 ±      3218.885  ops/s
StringLoopJmhBenchmark.utf8LenByLoop        UTF16              10  thrpt    5  304994614.456 ±  39946589.721  ops/s
StringLoopJmhBenchmark.utf8LenByLoop        UTF16             100  thrpt    5   87963328.389 ±   7517439.796  ops/s
StringLoopJmhBenchmark.utf8LenByLoop        UTF16            1000  thrpt    5   10894858.166 ±   2268465.202  ops/s
StringLoopJmhBenchmark.utf8LenByLoop        UTF16          100000  thrpt    5      28255.579 ±      3497.730  ops/s```

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### Progress
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### Issue
 * [JDK-8372353](https://bugs.openjdk.org/browse/JDK-8372353): API to compute the byte length of a String encoded in a given Charset (**Enhancement** - P4)


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