Native: provide extensions to read/write data from memory referred by a C-ptr

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On native, data could be read or written from/to native memory.
Currently, there's no built-in API to work with native memory, so users have to roll out their own:

• https://github.com/ktorio/ktor/blob/c9f58b1bd75c735d335dfaa9ca1a09ff9b1d7766/ktor-io/posix/src/io/ktor/utils/io/core/BytePacketBuilderOperations.posix.kt#L16
• https://github.com/ktorio/ktor/blob/c9f58b1bd75c735d335dfaa9ca1a09ff9b1d7766/ktor-io/posix/src/io/ktor/utils/io/Input.posix.kt#L16

It would be nice to provide such functionality out of the box.

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Drafted an implementation: https://github.com/Kotlin/kotlinx-io/pull/450/files
However, I'm in doubts how useful this API will be (because I'm struggling with providing meaningful samples for it :) ).