This increases the likelihood that HTTP/2 connections will be shared.
 *  New: Authentication challenges and credentials now use a charset. Use this in
    your authenticator to support user names and passwords with non-ASCII
    characters.
 *  New: Accept a charset in `FormBody.Builder`. Previously form bodies were
    always UTF-8.
 *  New: Support the `immutable` cache-control directive.

    val call =
      client.newCall(
        Request(
          url = server.url("/foo"),
          body =
            object : RequestBody() {
              override fun contentType(): MediaType = "text/plain; charset=utf-8".toMediaType()

              override fun writeTo(sink: BufferedSink) {
                sink.write(postBytes)
              }
            },
        ),
      )
    val response = call.execute()

	public final fun -deprecated_type ()Ljava/lang/String;
	public final fun charset ()Ljava/nio/charset/Charset;
	public final fun charset (Ljava/nio/charset/Charset;)Ljava/nio/charset/Charset;
	public static synthetic fun charset$default (Lokhttp3/MediaType;Ljava/nio/charset/Charset;ILjava/lang/Object;)Ljava/nio/charset/Charset;
	public fun equals (Ljava/lang/Object;)Z