If its the command buffer's first call to vkBeginCommandBuffer, we must
*initialize* the command buffer's state. Otherwise, we must *reset* its
state. In both cases, let's use anv_ResetCommandBuffer.
From the Vulkan 1.0 spec:
If a command buffer is in the executable state and the command buffer
was allocated from a command pool with the
VK_COMMAND_POOL_CREATE_RESET_COMMAND_BUFFER_BIT flag set, then
vkBeginCommandBuffer implicitly resets the command buffer, behaving
as if vkResetCommandBuffer had been called with
VK_COMMAND_BUFFER_RESET_RELEASE_RESOURCES_BIT not set. It then puts
the command buffer in the recording state.
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