class FramebufferAllocator

Obtain a cached Framebuffer, or lazily create a new one if necessary. Creating a VkFramebuffer

requires a VkRenderPass; if necessary the render pass will also be created lazily, but only if

|allow_render_pass_creation| is true (otherwise a CHECK will fail). This allows the

application to require all render passes to be created at specific times (e.g. startup, or

loading a particular game level) to avoid jank due to lazy creation of render passes (and

pipelines).

NOTE: pipelines cannot be created without a render pass, and render passes are useless without

a pipeline. Therefore, we could allow lazy render pass creation and rely on the inevitable

failed CHECK during pipeline creation. However, it is better to also disallow render pass

creation because then the source of the problem is obvious, not lost among the many other

reasons that might trigger lazy pipeline creation.