Add ContextWgpu methods for managing current render pass For simplicity ensureRenderPassStarted() just ends the current render pass and starts a new one. Bug: angleproject:8582 Change-Id: I929526cf2574fa33309310e7f60191c10ab3bf7a Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/5388075 Commit-Queue: Matthew Denton <mpdenton@chromium.org> Reviewed-by: Liza Burakova <liza@chromium.org> Reviewed-by: Shahbaz Youssefi <syoussefi@chromium.org>