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)

Merge branch 'master' into docking ...

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

IO: changed AddInputCharacter(unsigned short c) signature to AddInputCharacter(unsigned int c). ...

Examples/Backends: Don't filter characters under 0x10000 before calling io.AddInputCharacter(), the filtering is done in io.AddInputCharacter() itself. This is in prevision for fuller Unicode support. (#2538, #2541)

Merge branch 'master' into docking ...

# Conflicts:
#	examples/example_sdl_opengl2/main.cpp
#	examples/example_sdl_opengl3/main.cpp
#	examples/example_sdl_vulkan/main.cpp
#	examples/imgui_impl_sdl.cpp
#	examples/imgui_impl_sdl.h
#	imgui.cpp

Examples: SDL: Gamepad support minor amend. Fixes ImGuiBackendFlags_HasGamepad not being set. Enable in Emscripten demo. Tweaks. (#2509, #2484).

Merge branch 'master' into docking ...

# Conflicts:
#	examples/example_win32_directx11/main.cpp
#	examples/example_win32_directx12/main.cpp
#	examples/example_win32_directx9/main.cpp
#	imgui.cpp

Fix typos. (#2413)

Merge branch 'master' into docking ...

# Conflicts:
#	imgui.cpp
#	imgui.h

Examples: Extracted gamepad code into ImGui_ImplGlfw_UpdateGamepads(). Renamed matching Win32 function for consistency. ...

Added more link to nothing's oversample document. Spacing bits.

Examples: Win32: Removed unused code left-over from merge e9c625a

Examples: Made imgui_impl_win32 drag gdi32.lib for GetDeviceCaps(). (#2327)

Viewport: Added ImGuiViewportFlags_NoFocusOnClick + support in imgui_impl_win32. Made windows with no decoration always set the _NoFocus flags. (#1542, #2117) ...

Fix e.g. clicking on protruding combo box stealing highlight from parent window with decoration.

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 'master' into viewport ...

# Conflicts:
#	examples/imgui_impl_win32.cpp

Examples: Win32: Added support for mouse buttons 4 and 5 via WM_XBUTTON* messages. (#2264)

Examples: Win32: Fix for older Windows SDK.

Merge branch 'master' into viewport ...

# Conflicts:
#	docs/CHANGELOG.txt
#	examples/imgui_impl_win32.cpp
#	imgui_demo.cpp

Examples: Win32: Using IsChild() to be compatible with windows created within a parent. (#1951, #2087, #2156, #2232)

Merge branch 'master' into viewport ...

# Conflicts:
#	docs/CHANGELOG.txt
#	examples/imgui_impl_win32.cpp
#	examples/imgui_impl_win32.h

Examples: Win32: Added support for XInput games (if ImGuiConfigFlags_NavEnableGamepad is enabled).

Examples: Win32: Using GetForegroundWindow() instead of GetActiveWindow() to be compatible with windows created in a different thread. (#1951, #2087, #2156, #2232) [many people]

Viewport: Added ImGuiWindowClass / SetNextWindowClass() (concept imported from Docking ImGuiDockFamily), which currently allows to overwrite viewport flags on a per-window basis. Exposed FindViewportByID(). Win32: Support for ParentViewportId. (#1542)

Viewport: Win32: Workaround to the fact that ::WindowFromPoint() seems to return Windows using ImGuiViewportFlags_NoInputs / HTTRANSPARENT when dragging nearby the platform title bar. This is to allow using platform decoration. I don't understand this well atm. (#1542)

Viewport: Added Platform_UpdateWindow hook for general purpose: Rework Win32 code to reflect viewport flags changes into Win32 while the window is active.

Merge branch 'master' into viewport ...

# Conflicts:
#	examples/imgui_impl_sdl.cpp

Tweaked asserts

Viewport, DPI: Now using DpiScale from the ImGuiPlatformMonitor array instead of calling Platform_GetWindowDpiScale() before the platform window creation. Might even tentatively see if things work out without Platform_GetWindowDpiScale. (#1676)

Viewport: Win32, GLFW, SDL: Clarified back-ends by using global mouse position direction. GLFW: disabled io.MouseHoveredViewport setting under Mac/Linux. (#1542, #2117) + various comments.

About, IO: Added io.BackendPlatformName, io.BackendRendererName for informational/QA purpose.