Description

Reworked the timeline semaphore sample to prevent it crashing on Windows.

The only obvious trigger for the crash that I could observe was the main thread calling "vkDeviceWaitIdle" whilst the compute thread was in "wait_timeline_gpu". To avoid this, I removed the "wait/signal_timeline_gpu" calls (opting to attach the "VkTimelineSemaphoreSubmitInfo" to the queue submissions instead), and restructured the compute/graphics work stages to prevent the compute thread running ahead and submitting (potentially blocking) work.

• Replaced the "wait/signal_timeline_gpu" calls with "VkTimelineSemaphoreSubmitInfo" added to the queue submissions
• Added an enum for identifying the timeline stages, to make it easier to read and debug the signals/waits
• Moved the rendering work to a seperate thread, leaving the main thread responsible for acquiring and presenting the swapchain image, and signalling the timeline semaphore.

Fixes KhronosGroup#588

Tested on Windows
Tested using seperate and shared queue for compute and graphics

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