#15232)

…sabled

Motivation:

We should always prefer direct buffers if the ByteBufAllocator
implementations are pooled as deallocating these buffers should be rare.

Modifications:

- Add new method to PlatformDependent that can be used to check if
default direct buffer usage was explicit disabled
- Use this method in our pooled ByteBufAllocator implementations to
check if we should use direct buffers or not by default

Result:

Less memory copies and better performance when using the pooled
allocators even if Unsafe can not be used.