Update how the DTLS role is queried and reported.

Update DataChannelController to query the DtlsTransport transport
directly for the SSL role instead of sending the request through
PeerConnection, JsepTransportController, JsepTransport and eventually
DtlsTransport. This reduces unnecessary coupling and threading checks
for several of the classes (most importantly PeerConnection and
JsepTransportController) and simplifies the PeerConnection interface by
removing the redundant method, associated mocks and fakes.

While making this change, also update SctpTransport to query its
internal DTLS transport directly for the role.

Lastly, DtlsTransport is adjusted to ensure role information is
correctly propagated during state changes, not only for the
`DtlsTransportState::kConnected` state so that Information() returns up
to date information.

The change also clarifies threading requirements in the
JsepTransportController.

Bug: none
Change-Id: If925416c589c52ceef1d20ffe58b72fa59f7d496
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/463540
Commit-Queue: Tomas Gunnarsson <tommi@webrtc.org>
Reviewed-by: Harald Alvestrand <hta@webrtc.org>
Auto-Submit: Tomas Gunnarsson <tommi@webrtc.org>
Cr-Commit-Position: refs/heads/main@{#47420}