Fix data channel ID reuse race condition

When a peer reopens a data channel quickly after closing it, the Host
might receive the new OPEN message while the old channel is still in
kClosing state (waiting for the Client's ACK to complete the reset).
This causes the Host to reject the OPEN message because the SID is
still marked as reserved.

This fix forcefully closes the old channel if it is in kClosing state
and we receive a new OPEN message for the same SID, allowing the new
channel to be created successfully.

Also includes a reproduction test in data_channel_controller_unittest.cc.

Bug: chromium:480916451
Change-Id: Ie181a110f5d23561dcd90fbc63676f18040a7429
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/485180
Reviewed-by: Harald Alvestrand <hta@webrtc.org>
Commit-Queue: Tomas Gunnarsson <tommi@webrtc.org>
Cr-Commit-Position: refs/heads/main@{#48081}