Addendum to #2635. Add support for multi-viewports in SDL+DX!! example. making all Win32-centric back-ends handle PlatformHandleRaw. Using the field to use/store the HWND for internal purpose in SDL/GLFW back-ends. (#1542)

Synced/merged minor cruft from master branch to minimize drift. Only meaningful change AFAIK is removing ImGuiComboFlags_PopupAlignLeft flag from the tab list combo emitted by TabBar.

Merge branch 'master' into docking ...

# Conflicts:
#	examples/imgui_impl_dx10.cpp
#	examples/imgui_impl_dx11.cpp
#	examples/imgui_impl_dx9.cpp
#	examples/imgui_impl_opengl3.cpp
#	imgui.h
#	imgui_demo.cpp

Renamed ImGuiBackendFlags_HasVtxOffset to ImGuiBackendFlags_RendererHasVtxOffset to match naming convention already used in viewport/docking branch. (#2591) + Fix OpenGL3 code missing flag.

Merge branch 'master' into docking ...

# Conflicts:
#	examples/imgui_impl_dx10.cpp
#	examples/imgui_impl_dx10.h
#	examples/imgui_impl_dx11.cpp
#	examples/imgui_impl_dx11.h
#	examples/imgui_impl_dx9.cpp
#	examples/imgui_impl_dx9.h
#	examples/imgui_impl_opengl3.cpp
#	examples/imgui_impl_opengl3.h
#	examples/imgui_impl_osx.h
#	examples/imgui_impl_osx.mm
#	imgui.cpp
#	imgui.h
#	imgui_demo.cpp
#	imgui_internal.h

Examples/Backends: DirectX9/10/11/12, Vulkan, OpenGL3 (Desktop GL only): Added support for large meshes (64k+ vertices) with 16-bits indices, enable 'ImGuiBackendFlags_HasVtxOffset' config flag in back-end. (#2591)

Merge branch 'master' into docking ...

# Conflicts:
#	examples/imgui_impl_dx10.cpp
#	examples/imgui_impl_dx11.cpp
#	examples/imgui_impl_dx12.cpp
#	examples/imgui_impl_dx9.cpp
#	examples/imgui_impl_opengl2.cpp
#	examples/imgui_impl_opengl3.cpp
#	examples/imgui_impl_vulkan.cpp
#	imgui.cpp

Examples: Added missing per-renderer local changelogs. (#2037, #1639, #2452)

ImDrawCallback_ResetRenderState, Examples: Added support for reset render state callback. (#2037, #1639, #2452)

Merge branch 'vulkan_fix_master' into vulkan_fix_docking

Vulkan: Bits. Using IM_ALLOC/IM_FREE instead of new[] / delete[].

Vulkan, Viewports: ImGui_ImplVulkan_RenderDrawData and renderer back-end automatically manage ImGui_ImplVulkanH_WindowRenderBuffers for each viewports so user doesn't have to do it. (#2461, #2348, #2378, #2097)

Merge branch 'vulkan_fix_master' into vulkan_fix_docking (WARNING: as is the validation layer will error on same vertex/index buffer being used for all frames) ...

# Conflicts:
#	examples/imgui_impl_vulkan.cpp
#	examples/imgui_impl_vulkan.h

Vulkan: Removed superfluous vkInstance parameters being passed along.

Vulkan: Removed requirement for user to pass their own render buffer storage to ImGui_ImplVulkan_RenderDrawData(), this is managed internally.

Vulkan: Added ImageCount to InitInfo structure (!= MinImageCount) will be needed for viewports. Renamed FramesQueueSize -> ImageCount. (#2472, #2071)

Vulkan, Viewports: Fix for resizing viewport windows crashing. (#2472)

Vulkan, Viewports: Fix for resizing viewport windows crashing. (#2472)

Vulkan, Viewports: Fixed ImGui_ImplVulkan_SetWindowSize() not recreating command-buffers, fence etc. (#2472, #2461, #2071)

Vulkan: Note for unsupported feature with multi-viewports. (#2071)

Vulkan: Viewports: Removed redundant field.

Merge branch 'vulkan_fix_master' into vulkan_fix_docking ...

# Conflicts:
#	examples/imgui_impl_vulkan.cpp

Vulkan: Renaming demo/helper structures. Tidying up examples main.cpp.

Vulkan: Renaming, we want InitInfo to source MinImageCount which is the "source" value (so viewport creation can use this). Made ImGui_ImplVulkan_DestroyFrameRenderBuffers public. (#2071)

Vulkan: Storing user info into a single g_VulkanInitInfo structure to simplify code.

Vulkan: Added extra parameter to ImGui_ImplVulkan_RenderDrawData(). User is in charge of owning/storing 1 ImGui_ImplVulkan_FrameRenderBuffers per in-flight rendering frame. Removed ImGui_ImplVulkan_SetFramesQueueSize. (#2461, #2348, #2378, #2097, #2071, #1677)

Vulkan: More renaming. Comments.

Examples: Vulkan: Merged helpers into ImGui_ImplVulkanH_CreateWindowData. Removed ImGui_ImplVulkan_InvalidateFrameDeviceObjects from API. Comments. (#2071)

Examples: Vulkan: Renamed QueuedFramesCount to FramesQueueSize. Moved Framebuffer, Backbuffer to FrameData structure. (#2071)

Examples: Vulkan: Updated Changelog, removed debug code, tweaked code, made GLFW/SDL match each others. Initialize FrameDataForRender fields. Added Assertion. Clearing fields on DestroyFrameData(). (#2071)