[embedder] Vulkan embedder incorrectly queries vkGetInstanceProcAddr without the vk prefix

[nanokatze]

See https://github.com/flutter/engine/blob/main/shell/platform/embedder/embedder.cc#L565 and how things are passed down to glfwGetInstanceProcAddr at https://github.com/flutter/engine/blob/main/examples/vulkan_glfw/src/main.cc#L394

This does make me wonder whether the Vulkan GLFW example ever worked at all?

[chinmaygarde]

I believe the VK prefix is not present for all proc addresses. If so, I am not sure how the example worked before. cc @bdero who authored the example before.

But we should fix this behavior and document it either way. Perhaps by trying both the suffixed version and the plain one.

[nanokatze]

I believe the VK prefix is not present for all proc addresses.

vkGetInstanceProcAddr is the only function that vulkan_get_instance_proc_address is used to get. All others are obtained through the newly obtained vkGetInstanceProcAddr or vkGetDeviceProcAddr.

I have submitted a PR that fixes this (see a mention above.) Tests weren't catching this because they set up get_instance_proc_address_callback to just always return vkGetInstanceProcAddr, which worked because that's the only function that get_instance_proc_address_callback was used for.

[bdero]

I authored both the Vulkan embedder API and the Vulkan GLFW embedder example; both run fine on Mac/Linux/Windows. Unfortunately, we don't have runtime CI checks for any of these GLFW examples (they just get compiled), and so runtime breakages get discovered lazily right now.

I believe this PR likely broke the embedder? (FYI @iskakaushik): flutter/engine@ff05a31#diff-37c8701cb24b47259df5ef2673e076c7fa7d04feacef849ab8b835ed1bfa991cR561

[github-actions]

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