Use a simple queue to combine literal string writes into one.

This should be able to combine all literal writes into single writes. It produces output like:

```go
	if mj.ABool {
		buf.WriteString(`{"ABool":true`)
	} else {
		buf.WriteString(`{"ABool":false`)
	}
	buf.WriteString(`, "BytesSent":`)
	fflib.FormatBits(&scratch, buf, uint64(mj.BytesSent), 10, false)
	buf.WriteString(`, "OriginId":`)
	fflib.FormatBits(&scratch, buf, uint64(mj.OriginId), 10, false)
	buf.WriteString(`, "RemoteIp":`)
	fflib.WriteJsonString(buf, mj.RemoteIp)
	buf.WriteString(`, "ReqId":`)
	fflib.WriteJsonString(buf, mj.ReqId)
	buf.WriteString(`, "ServerIp":`)
	fflib.WriteJsonString(buf, mj.ServerIp)
	buf.WriteByte('}')
```