Introduce rawPath in RequestTarget

[yzfeng2020]

The request path is normalized as part of the process here: https://github.com/line/armeria/blob/ce8a5ef3c2e87ec6fb6d8e21d07ea52d411654c1/core/src/main/java/com/linecorp/armeria/internal/common/ArmeriaHttpUtil.java#L615.

From the discord discussion we propose to add a new rawPath() method to the RequestTarget interface and subsequently expose it via ServiceRequestContext to retrieve the unmodified path. This could be useful in cases where we need the exact request path as sent by the client.

[yzfeng2020]

I will try to implement it!