use varhandles to to improve perf in Protobuf Parser and Generator

[pjfanning]

I added a benchmark to https://github.com/pjfanning/jackson-bench

Parser (Java 17.0.19)

Benchmark                                                            Mode  Cnt    Score    Error  Units
ProtobufDoubleArrayBench.benchParseFromByteArray                    thrpt    5  530.238 ± 31.017  ops/s
ProtobufDoubleArrayBench.benchParseFromByteArrayPacked              thrpt    5  618.494 ± 39.344  ops/s
ProtobufDoubleArrayBench.benchParseFromByteArrayPackedSwar          thrpt    5  740.256 ± 21.603  ops/s
ProtobufDoubleArrayBench.benchParseFromByteArraySwar                thrpt    5  630.836 ± 16.628  ops/s

Generator (Java 17.0.19)

Benchmark                                                                Mode  Cnt     Score     Error  Units
ProtobufDoubleArrayGenBench.benchGenerateToByteArray                    thrpt    5  1089.258 ±  22.509  ops/s
ProtobufDoubleArrayGenBench.benchGenerateToByteArrayPacked              thrpt    5  1189.129 ±  20.055  ops/s
ProtobufDoubleArrayGenBench.benchGenerateToByteArrayPackedSwar          thrpt    5  1787.496 ± 198.869  ops/s
ProtobufDoubleArrayGenBench.benchGenerateToByteArraySwar                thrpt    5  1822.569 ±  32.360  ops/s

[github-actions]

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