Examples: Vulkan: Moved CreateOrResizeWindowData func to imgui_impl_vulkan.h

Examples: Vulkan: Moved main.cpp data structures to imgui_impl_vulkan.h as shared helpers for the benefit of both the example and the platform/viewport renderer interface.

Viewport: Replaced UpdatePlatformWindows/RenderPlatformWindows by RenderAdditionalViewports(). The update is always called in EndFrame(). (#1542)

Examples: Vulkan: Moved variables into per-window data, refactored/tweaks to that the bug functions main.cpp for both SDL and GLFW examples match (they'll probably be moved to imgui_impl_vulkan as helpers).

Examples: Vulkan: Fix 7b968b0

Examples: Vulkan: Reduced duplicate code by skipping present on the first frame. Amend 201d589 by @ParticlePeter

Examples: Vulkan: Various tweak. Misc refactor into per-frame data. Duplicate buffer creation code moved to CreateOrResizeBuffer().

Merge branch 'examples_refactor' into viewport ...

# Conflicts:
#	examples/directx10_example/main.cpp
#	examples/directx11_example/main.cpp
#	examples/directx12_example/main.cpp
#	examples/opengl3_example/main.cpp
#	examples/sdl_opengl2_example/main.cpp
#	examples/sdl_opengl3_example/main.cpp
#	examples/sdl_vulkan_example/main.cpp
#	examples/vulkan_example/main.cpp
#	imgui.h

Examples: Vulkan: SDL: Fixed missing resize handler (not properly merged from #1367) + tweaks.

Examples: Vulkan: Moved code into shared helpers: ImGui_ImplVulkan_SelectSurfaceFormat, ImGui_ImplVulkan_SelectPresentMode.

Examples: Vulkan: Various tweaks to name variable more consistently like Vulkan + a few comments + a few imgui style code compaction.

Examples: Vulkan: Debug report tweak + always enable in Debug build.

Examples: Fixed enabling IMGUI_VULKAN_DEBUG_REPORT which was broken during refactor because of duplicate 'extensions' local variable.

Renamed ImGuiNavFlags io.NavFlags to ImGuiConfigFlags io.ConfigFlags. (#787)

Renamed ImGuiNavFlags io.NavFlags to ImGuiConfigFlags io.ConfigFlags. (#787)

Examples: NULL pointers for consistency.

Examples: SDL: Initial attempt at implementing the viewport/platform api. (WIP/test API) (#1542) ...

ImGui_ImplSDL2_Init() now takes a SDL GL context.

Examples: Added SDL+Vulkan example, the abstraction worked here :) (ref #1367)