Small optimization on "deserialization" and fix on benchmarks again

[paulovap]

• Fix benchmark run after change in flatbuffers-java deps
  Commit 6e214c3 fixes Kotlin build,
  but makes the kotlin-benchmark plugin misses the java classes at
  runtime, causing NotClassFoundError. The alternative to solve the issue
  is to read java's pom.xml to get the latest java version and use it
  as dependency. With that we avoid compilation errors on a new version and
  keep benchmark plugin happy.
• Remove redundant assign() method (use init() instead)
• Small optimizations and benchmark on deserialization

[paulovap]

jvm summary:
Benchmark                                          Mode  Cnt         Score         Error  Units
FlatbufferBenchmark.monstersDeserializationJava    avgt    5  60202904,433 ± 2571267,473  ns/op
FlatbufferBenchmark.monstersDeserializationKotlin  avgt    5  63491321,720 ±  582610,015  ns/op
FlatbufferBenchmark.monstersSerializationJava      avgt    5  43302673,950 ±  195710,100  ns/op
FlatbufferBenchmark.monstersSerializationKotlin    avgt    5  46153101,229 ±   87102,836  ns/op

This is the latest from benchmark, for some reason a couple of commits were missing for #7969 although it was pushed 🤷