Adds ImageUsageType to ImageClient and ImageContainer to identify user of Image at WebRenderImageHost.
Some ImageContainers are used only for allocating Image. Only following types calls ImageContainer::SetCurrentImages().
- ImageUsageType::Canvas
- ImageUsageType::OffscreenCanvas
- ImageUsageType::VideoFrameContainer
Differential Revision: https://phabricator.services.mozilla.com/D211147