Use std::span in ToRtpCapabilities

Make ToRtpCapabilities take std::span<const Codec> and
std::span<const RtpHeaderExtensionCapability> instead of vector.

Rename GetDefaultEnabledRtpHeaderExtensions to
GetDefaultEnabledRtpHeaderCapabilities and make it return
std::vector<RtpHeaderExtensionCapability> instead of RtpExtension.
Remove the old GetDefaultEnabledRtpHeaderExtensions.

Update tests and callers to match the new signatures.
In voice engine test, convert capabilities to extensions when needed.

Bug: webrtc:514817938
Change-Id: I742abe7c3459ffb48466129dbec914ccb659cbe5
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/479801
Reviewed-by: Danil Chapovalov <danilchap@webrtc.org>
Commit-Queue: Harald Alvestrand <hta@webrtc.org>
Cr-Commit-Position: refs/heads/main@{#47933}