Adds a new StatExposureCriteria for non-standard stats. This removes the virtual call to is_standardized() which can simply use the StatExposureCriteria. Bug: webrtc:14546 Change-Id: If4174019ff8cc6559ab0dc9a04e0f8a6631b9842 Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/279045 Reviewed-by: Harald Alvestrand <hta@webrtc.org> Reviewed-by: Henrik Boström <hbos@webrtc.org> Commit-Queue: Evan Shrubsole <eshr@webrtc.org> Reviewed-by: Mirko Bonadei <mbonadei@webrtc.org> Cr-Commit-Position: refs/heads/main@{#39057}