Android: Move common functions from VideoRendererGui to new RendererCommon file

This is primarily done to prepare for a new renderer implementation.

BUG=webrtc:4742
R=glaznev@webrtc.org

Review URL: https://codereview.webrtc.org/1298673002 .

Cr-Commit-Position: refs/heads/master@{#9742}
5 files changed