This structure is used outside Dlrr creating/parsing.
but RTCPReceiveTimeInfo structure doesn't follow naming style.
rtcp::ReceiveTimeInfo added to replace both Dlrr::SubBlock (when creating/parsing packets)
and RTCPReceiveTimeInfo (for other uses).
this CL is a split of https://codereview.webrtc.org/1557593002/
BUG=webrtc:5260
R=asapersson@webrtc.org, åsapersson
Review URL: https://codereview.webrtc.org/1631683002 .
Cr-Commit-Position: refs/heads/master@{#11380}
