Consider emitting hex for content-based byte arrays in `toString`

[JakeWharton]

ByteArray.contentToString() output is... not great. Emitting hexidecimal is probably more in line with what someone would expect.

This is blocked on HexFormat and its APIs (e.g., toHexString()) going stable.

[drewhamilton]

For reference:

@Poko class ByteThing(
    val byteA: Byte,
    val byteB: Byte,
    val byteC: Byte,
    val byteD: Byte,
    @ArrayContentBased val byteArray: ByteArray,
)

val sample = ByteThing(
    byteA = 0.toByte(),
    byteB = 127.toByte(),
    byteC = 128.toByte(),
    byteD = 255.toByte(),
    byteArray = byteArrayOf(
        0.toByte(),
        127.toByte(),
        128.toByte(),
        255.toByte(),
    ),
)

println(sample) // ByteThing(byteA=0, byteB=127, byteC=-128, byteD=-1, byteArray=[0, 127, -128, -1])

[JakeWharton]

Another option would be to have a @PublishedApi internal function for the conversion for the time being.

Right now I'm doing

for (byte in bytes) {
  append(byte.toUByte().toString(16).padStart(2, '0'))
}