Add WPT for inbound-rtp existing for early media use cases.

Web test equivalent of [1]. Since we never set the SDP answer, the only
thing that can convey the SSRC information is the reception of an RTP
packet which causes the "inbound-rtp" to appear (whether or not field
trial "WebRTC-RTP-Lifetime" is enabled).

Note that Mac bots are expecting to "[ Failure Pass ]" here because of
https://crbug.com/441912460 but the TestExpectations already reflects
this and is not anything new with this test specifically.

[1] https://webrtc-review.googlesource.com/c/src/+/406521

Bug: chromium:406585888
Change-Id: I538640d3fe64f09e78ddee1e3502d7ad1195057f
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6889571
Auto-Submit: Henrik Boström <hbos@chromium.org>
Reviewed-by: Harald Alvestrand <hta@chromium.org>
Commit-Queue: Harald Alvestrand <hta@chromium.org>
Commit-Queue: Henrik Boström <hbos@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1509022}