[Java] Remove usage of PlatformDependent in arrow-vector

[gf2121]

Describe the enhancement requested

For some reason our system need to set netty param io.netty.noUnsafe=true. We have replaced arrow-memory-netty with arrow-memory-unsafe. But there are still some utils in arrow-vector like DictionaryEecoder, VectorSchemaRootAppender using PlatformDependent which will cause NullPointerException when io.netty.noUnsafe=true .

IMO netty params should not affect the work of arrow-vector, can we replace the usage of PlatformDependent by ArrowBuf#setxxx ?

Component(s)

Java