examples/vulkan: add optional dynamic rendering support

[qiyuewuyi2333]

Related issue: #9340

Add opt-in dynamic rendering support to all four Vulkan examples
(glfw, sdl2, sdl3, win32) via a commented-out macro at the top of
each main.cpp:

//#define APP_USE_DYNAMIC_RENDERING

When enabled:

• Requests VK_KHR_dynamic_rendering (and its dependencies) at device
  creation and enables the VkPhysicalDeviceDynamicRenderingFeaturesKHR
  feature.
• Loads vkCmdBeginRendering/vkCmdEndRendering at runtime via
  vkGetDeviceProcAddr (falls back to the KHR suffixed variants for
  pre-1.3 drivers).
• Sets wd->UseDynamicRendering = true before
  ImGui_ImplVulkanH_CreateOrResizeWindow so the helper skips
  RenderPass/Framebuffer creation.
• Configures ImGui_ImplVulkan_InitInfo with UseDynamicRendering=true
  and PipelineRenderingCreateInfo (using the actual surface format)
  for both main and viewport pipelines.
• Replaces vkCmdBeginRenderPass/vkCmdEndRenderPass in FrameRender
  with vkCmdBeginRendering/vkCmdEndRendering plus the required
  image layout transitions (PRESENT_SRC_KHR <-> COLOR_ATTACHMENT_OPTIMAL).

When the macro is not defined the examples behave exactly as before.

[qiyuewuyi2333]

Actually, it's more better if the backend support handle with dynamic rendering for main window like muti-window does.
But that will be a much more impact. So I think just adjusting it in example is acceptable.

[ocornut]

Note that both #5446 and #8600 had code to enable dynamic rendering in examples. I've attached the latest patch version for both for references. You can probably compare your code to them. They seem simpler?

[qiyuewuyi2333]

Note that both #5446 and #8600 had code to enable dynamic rendering in examples. I've attached the latest patch version for both for references. You can probably compare your code to them. They seem simpler?

Thx for your references. I have compared my code to both patches and simplified accordingly as below:

• Remove the global function pointers and replace it with static local variable
• Simplified ImGui_ImplVulkan_InitInfo
  One difference I kept: I'm using vkGetDeviceProcAddr instead of vkGetInstanceProcAddr to load vkCmdBeginRenderingKHR/vkCmdEndRenderingKHR, since these are device-level commands. This was also noted by @ChrisTom-94 in Fix Vulkan validation error during window detach in multi-viewport mode (#8176) #8600.

I also applied the same changes to all four Vulkan examples (glfw, sdl2, sdl3, win32) for consistency.