Vulkan: Updates to onFramebufferBoundary 1. Rename to the more appropriate onFrameBoundary 2. Add method to renderer for better encapsulation 3. When being moved to the background some apps unMakeCurrent the contexts and exit without calling other frame boundary APIs. Handle such usecases by treating ContextVk::onUnMakeCurrent(...) as a frame boundary Bug: angleproject:386749841 Change-Id: Ic2a8ecb631d132d99f8508f45f3b454c49f6624e Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/7004936 Reviewed-by: Shahbaz Youssefi <syoussefi@chromium.org> Commit-Queue: mohan maiya <m.maiya@samsung.com> Reviewed-by: Charlie Lao <cclao@google.com>