Deinitialize PLS planes when their texture is deleted The spec originally called for PLS planes to be converted to memoryless when their texture was deleted, but this is not compatible with WebGL, which does not support memoryless planes. Change the behavior to deinitialize them instead. This change requires the addition of a new observer message, angle::SubjectMessage::TextureIDDeleted, which PLS uses to deinitialize a plane when the app deletes its texture. Bug: chromium:1421437 Change-Id: I58fd91003747160f0a1abc1a8a7a87668890ba1f Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/4518565 Reviewed-by: Shahbaz Youssefi <syoussefi@chromium.org> Commit-Queue: Chris Dalton <chris@rive.app>