Add checks to ensure encoder is not used below API level 19. Removes global @TargetApi from MediaCodecUtils since it is also used by the decoder. Ensures that texture mode is never enabled below API level 18. Bug: webrtc:9821 Change-Id: I2ca1014bf8995719c970eb1449b0acbf7b3c883e Reviewed-on: https://webrtc-review.googlesource.com/c/103701 Reviewed-by: Paulina Hensman <phensman@webrtc.org> Commit-Queue: Sami Kalliomäki <sakal@webrtc.org> Cr-Commit-Position: refs/heads/master@{#24990}