Consider making DocumentSnapshot.encodedData() public?

[martinbonnin]

This is a follow up from #500

This also relates to Kotlin/kotlinx.serialization#2223

I also have dynamic content that can be different types:

{
  "value": "someValue"
}

vs

{
  "value": {
    "version": 0,
    "content": "someValue"
  }
}

The only way I found to make it work is to use the internal API:

@file:Suppress(
    "CANNOT_OVERRIDE_INVISIBLE_MEMBER",
    "INVISIBLE_MEMBER",
    "INVISIBLE_REFERENCE",
)

val data = documentSnaphshot.encodedData()

data as Map<String, Any?>
data.forEach {
    if (it.value is String) {
        // case 1
    } else if (it.value is Map<*, *>) {
        // case 2
    } else {
        error("expected a string or a map")
    }
}

From #500 (comment), I understand, this is currently dangerous because the returned data contains native NativeTimestamp values that have different types in commonMain but could those be updated to always return dev.gitlive.firebase.firestore.Timestamp instead?