Add getters for &ServiceRequest

[junbl]

PR Type

Feature

PR Checklist

• Tests for the changes have been added / updated.*
• Documentation comments have been added / updated.
• A changelog entry has been made for the appropriate packages.
• Format code with the latest stable rustfmt.
• (Team) Label with affected crates and semver status.

*no tests necessary; none for parts_mut/into_parts or other getters

Overview

Adds getters for cases when you only have a &ServiceRequest and need access to the inner parts.

• parts: returns immutable refs to the inner request and payload. Non-owning counterpart to into_parts and parts_mut.
• request: just gives access to the HttpRequest since there's not a lot you can do with a &Payload currently.

This allows access to parts of the HttpRequest not already covered by the existing getters. Additionally, this allows FromRequesting types that don't require access to the Payload, like Identity. (ServiceRequest::extract, while covering a similar use case, requires a &mut ServiceRequest and thus isn't usable in this context.)

No breaking changes.

Use case mentioned in #2175, but it doesn't seem like the associated issue was ever opened.

[robjtede]

Thanks