Move IceTransport ownership to DtlsTransport from JsepTransport

This patch refactors the ownership model between JsepTransport,
DtlsTransport, and IceTransport to simplify the object hierarchy.

Previously, `DtlsTransportInternal` held a raw pointer to
`IceTransportInternal`, while `JsepTransport` maintained ownership of,
but does not use, the `IceTransportInterface` object.

With this change, `DtlsTransportInternal` now accepts and stores a
`scoped_refptr<IceTransportInterface>`. This ensures that the DTLS
transport keeps the underlying ICE transport alive. Consequently,
`JsepTransport` no longer needs to hold explicit references to
`ice_transport_` and `rtcp_ice_transport_`, as they are now owned via
the DTLS transports.

Key changes:
* Update `DtlsTransportInternal` and `FakeDtlsTransport` to take
    `scoped_refptr<IceTransportInterface>` in their constructors.
* Remove direct ICE transport members from `JsepTransport`.
* Update `JsepTransportController` to pass reference-counted ICE
    transports when creating DTLS transports.
* Update unit tests and integration tests to use `make_ref_counted`
    for ICE transports and match the new constructor signatures.

Bug: webrtc:360058654
Change-Id: I6cd5015b6c9363091c1af37bea1d8cd779cea095
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/427682
Reviewed-by: Tony Herre <herre@google.com>
Commit-Queue: Tomas Gunnarsson <tommi@webrtc.org>
Cr-Commit-Position: refs/heads/main@{#46308}