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

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: 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)

Examples: Vulkan: Fixed tabs->space, removed extraneous braces and empty lines. (#2071)

Examples: Vulkan: Added calls to supports runtime changing back buffer count. (#2071)

Merge branch 'master' into docking

Tabs to Spaces, comments.

Merge branch 'master' into docking ...

# Conflicts:
#	examples/imgui_impl_opengl2.cpp
#	examples/imgui_impl_opengl3.cpp
#	imgui.cpp
#	imgui_widgets.cpp

Examples: SDL: Using the SDL_WINDOW_ALLOW_HIGHDPI flag. (#2306, #1676) [@rasky]

Merge branch 'viewport' into docking ...

# Conflicts:
#	docs/CHANGELOG.txt
#	imgui.cpp
#	imgui_draw.cpp

Merge branch 'master' into viewport ...

# Conflicts:
#	examples/example_sdl_vulkan/main.cpp
#	examples/imgui_impl_dx11.cpp
#	examples/imgui_impl_dx12.cpp
#	examples/imgui_impl_glfw.cpp
#	examples/imgui_impl_sdl.cpp
#	examples/imgui_impl_vulkan.h
#	imgui.cpp

Removed trailing spaces (#2038, #2299)

Merge branch 'viewport' into docking ...

# Conflicts:
#	examples/example_allegro5/main.cpp
#	examples/example_win32_directx9/main.cpp

Merge branch 'master' into viewport + added style tweak block when viewports are enabled ...

# Conflicts:
#	examples/example_glfw_opengl3/main.cpp
#	examples/example_sdl_opengl3/main.cpp
#	examples/example_win32_directx11/main.cpp

Examples: Setting up style before bindings, so in complex binding (vulkan/dx12) it isn't miles away from the context creation.

Merge branch 'viewport' into docking ...

# Conflicts:
#	docs/CHANGELOG.txt
#	imgui_widgets.cpp

Merge branch 'master' into viewport ...

# Conflicts:
#	imgui.cpp

Examples: SDL2+Vulkan: Fixed application shutdown which could deadlock on Linux + Xorg. (#2181)

Merge branch 'viewport' into docking ...

# Conflicts:
#	examples/example_allegro5/main.cpp
#	examples/example_marmalade/main.cpp

Merge branch 'master' into viewport + specific changes for GLFW callbacks ...

# Conflicts:
#	examples/example_glfw_opengl3/main.cpp
#	examples/example_win32_directx11/main.cpp
#	examples/example_win32_directx9/main.cpp
#	examples/imgui_impl_glfw.cpp

Examples: Misc comments mainly related to GLFW callbacks. (#1759)

Merge branch 'viewport' into docking

Merge branch 'master' into viewport ...

# Conflicts:
#	examples/imgui_impl_win32.cpp
#	examples/imgui_impl_win32.h
#	imgui.cpp

Examples: Vulkan: Fixed some minor discrepency in the SDL+Vulkan example to match the Glfw+Vulkan example. (cc #2097)