Credential hand-over to per-user server sessions

[Piclaw (piclaw-bot)]

Summary

This replaces and consolidates #1409, #1410, #1411, and #1412 into a single branch from rcarmo:wrdp.

The split PR heads use wrdp/* branch names, but the fork now uses the canonical wrdp branch. Because Git cannot keep both refs/heads/wrdp and refs/heads/wrdp/* at the same time, this PR carries the updated commits and review fixes together.

Why

wrdp follows the xrdp-sesman multi-user architecture model, so it needs a way to hand authenticated credentials from the protocol handshake into the per-user session binder.

Changes

• Adds an async post-auth connection binder hook in ironrdp-server.
• Scopes reactivation credential reuse to the current TCP connection.
• Exposes CredSSP delegated credentials to server consumers via the same Credentials shape used by ClientInfo.
• Restores the client-facing denial PDU on credential reject/backend-error paths before returning the error.
• Clarifies binder docs so they refer to authenticated credentials being available, not only to configured validator acceptance.
• Skips binder re-execution during deactivation/reactivation so resize/reactivation does not restart per-user binding or replace handlers mid-session.

Copilot review follow-up

This includes fixes for the Copilot comments from the superseded PRs:

• Credential hand-over to sub-servers (Wrdp/canonical stack) #1409: denial PDU regression and binder doc wording.
• Add post-auth connection binder hook #1411: binder should not run again during reactivation.
• Wrdp/reactivation credential cache #1412: denial PDU regression and reactivation rebinding.
• Expose CredSSP delegated credentials to servers #1410 had no inline Copilot review comments.

Validation

• cargo check -p ironrdp-server -p ironrdp-acceptor
• git diff --check