[WebRTC] Migrate more Legacy Natives to Proxy Natives

webrtc-review.googlesource.com/c/src/+/476440 migrated Legacy Natives
to Proxy Natives. However, we found that there is some Legacy Natives
remaining in some of the WebRTC's files. Therefore, this CL migrates
the remaining Legacy Natives to Proxy Natives.

Legacy Natives is basically using the "native" keyword in Java files
to specify Java->Native methods. Proxy Natives is when we use the
@NativeMethods annotation in Java files to specify Java->Native methods

Bug: chromium:40253109
Change-Id: I1d32455827ce44dd0e4a0f09dfcbc5e3ba565fa4
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/488160
Reviewed-by: Zoé Lepaul <zlep@webrtc.org>
Commit-Queue: Zoé Lepaul <zlep@webrtc.org>
Reviewed-by: Danil Chapovalov <danilchap@webrtc.org>
Cr-Commit-Position: refs/heads/main@{#48187}