Viewport: Render: Fix draw list build code to allow child windows to be in a different viewports (which will happen with e.g. extruding menus). (#1542)

Viewport: Shuffled code in Begin to reset size of reappearing popups prior to selecting viewport, to avoid mistakenly using an old size. Moved code out of UpdateSelectWindowViewport() to the section of Begin where positions is being locked down, to avoid code in-between duplicating this. (#1542)

Viewport: Moved ImGuiWindowFlags_FullViewport to an internal ViewportOwned flag. Renamed AddViewport to AddUpdateViewport. (#Viewport: Shuffled code in Begin to reset size of reappearing popups prior to selecting viewport, to avoid mistakenly using an old size. Moved code out of UpdateSelectWindowViewport() to the section of Begin where positions is being locked down, to avoid code in-between duplicating this. (#1542))

Viewport: Remove old code that never worked (testing wrong flag type, always false) + shuffled a few things in Begin() to clarify dependencies. Fixed viewport change on Begin/Begin/End/End patterns. (#1542)

Fix typos KeyDown => KeysDown

Documentation bits. Misc comments.

Viewport, Platform, DPI: Back-end store per-monitor DPI information in ImGuiPlatformMonitor. (#1542, #1676)

Viewport: Fix to allow changing/animated window name to be reflected in the OS e.g. task bar, so named documents can appear properly. (#1542)

Viewport: Fixed DPI changing viewport from interfering with moving another window (disabling code) + metrics crash fix on closed viewport window + Windows 10 call to SetThreadDpiAwarenessContext(DPI_AWARENESS_CONTEXT_PER_MONITOR_AWARE_V2) for DPI, with no noticeable improvements. (#1542, #1676)

Viewport: Virtual mouse position are patched immediately when viewports are moved in the virtual space, avoiding interaction glitchs on a resizing frame. (#1542)

Viewport: Debug/metrics tweaks + renaming comments

Fix minor error in doc ...

Not a big deal.

Viewport, Platform: Added ImGuiViewportFlags_TopMost that will be used by tooltip window (without it, clicking and holding the window emitting the tooltip would move the tooltip to the back) + GLFW backend fixes for non-win32 platforms. (#1542)

Merge branch 'master' into viewport ...

# Conflicts:
#	imgui.cpp
#	imgui_internal.h

Viewport: per-viewport overlay draw list created on demand. With this pattern it'll be easier to consider adding more (e.g. background draw list). (#545)

Internals: Popup: Moved popup/menu/tooltip positioning code (viewport branch needs it organized in a different manner, so we are pushing the bulk of it here to minimize differences).

Internals: Window: Aggregating ImDrawList into the ImGuiWindow structure.

Settings: Fixed saving an empty .ini file if CreateContext/DestroyContext are called without a single call to NewFrame(). (#1741)

NewFrame: Prevent division by zero in frame rate calculation if io.DeltaTime is continuously zero. (#1740, #881)

Viewport: Merged ImGuiPlatformData into ImGuiPlatformIO. Comments. (#1542)

Viewport, Platform: Added a way to register monitor bounds to imgui so they can be used to clamp individual-viewport tooltips/popups so they don't straddle monitors. (#1542)

Viewports, DPI: Renamed config flags. (#1542)

Viewport: Popups, Tooltips can individually request no task bar icons to the platform layer. (#1542)

Viewport: shuffled some code in the UpdateSelectWindowViewport() function.

Begin: moved tooltip position code in an else block. Misc comments

Internals: Renamed GetFrontMostModalRootWindow() to GetFrontMostPopupModal() and exposed in imgui_internal.h (#1738)

Examples, Platform, Viewport: Fixed inconsistent window ownership issues. Added comments. Made Win32/SDL back-ends track ownership.

Misc: IM_DELETE() helper function added in 1.60 doesn't clear the input _pointer_ reference, more consistent with expectation and allows passing r-value.

Merge branch 'master' into viewport ...

# Conflicts:
#	examples/imgui_impl_dx10.cpp
#	examples/opengl2_example/imgui_impl_glfw_gl2.cpp
#	examples/opengl3_example/imgui_impl_glfw_gl3.cpp
#	examples/vulkan_example/main.cpp
#	imgui.h

Version 1.61 WIP