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:
#	imgui.cpp
#	imgui_internal.h

Window: Fixed one case where auto-resize by double-clicking the resize grip would make either scrollbar appear for a single frame after the resize. Moved Scrollbar visibility block.

Internals: Moved scrollbar visibility calculation block below the call to UpdateManualResize(). This commit is _intended_ to have no side-effect (next commit will). Also moved ItemWidthDefault calculation below rectangles.

Scrollbar overlap an extra WindowBorderSize amount on the left to make all distances consistent. Reverted to BorderSize not affecting work/contents rectangles. Scrollbar, Style: Changed default style.ScrollbarSize from 16 to 14.

Internals: Minor no-op tidying up toward solving the WindowPadding / WindowBorderSize / ScrollbarSize overlapping mess. ...

+ Demo: Use SetScrollY().

Fixed newly created window (e.g. appearing child window) from having scrollbar active on the first frame. (fix 6e03b27) + reworded code a little. (+1 squashed commits) ...

Fixed auto-resize with AlwaysVerticalScrollbar or AlwaysHorizontalScrollbar flags not taking account of the expect scrollbar sizes.

Internals: Storing ScrollMax into a member. Mostly to facilitate debugging. Also locking down window->Scroll slightly lower in the Begin function.

TextWrapped, PushTextWrapPos(0.0f) within a window with horizontal scrolling from not covering the full horizontal area (previously only worked with an explicit contents size).

Internals: Renamed SizeContents to ContentSize, SizeContentsExplicit to ContentSizeExplicit. Tweaked Metrics->Show Rectangles functionality.

Window rectangles: Changed WorkRect to cover the whole region including scrolling (toward obsolete ContentsRegionRect) + using full WindowPadding*1 padding. ...

Tweaked InnerClipRect.
TreeNode, CollapsingHeader: Fixed highlight frame not covering horizontal area fully when using horizontal scrolling. (#2211, #2579)
TabBar: Fixed BeginTabBar() within a window with horizontal scrolling from creating a feedback loop with the horizontal contents size.
Columns: Fixed Columns() within a window with horizontal scrolling from not covering the full horizontal area (previously only worked with an explicit contents size). (#125)
Demo: Added demo code to test contentsrect/workrect

Clarified behavior of SetNextWindowContentSize(). Content size is defined as the size available after removal of WindowPadding on each sides. So SetNextWindowContentSize(ImVec2(100,100)) + auto-resize will always allow submitting a 100x100 item without creating a scrollbar, regarding of WindowPadding.The exact meaning of ContentSize for decorated windows was previously ill-defined.

Window rectangles: Made InnerRect not affected by window border sizes. its few users shouldn't be meaningfully affected.

Merge branch 'master' into docking

Comments (#2599). Moved branch Changelog above 1.71 wip one. Added some missing changelog bits.

Nav: Fixed rare crash when e.g. releasing Alt-key while focusing a window with a menu at the same frame as clearing the focus. This was in most noticeable in some back-ends with emits key release events when focusing another viewport. (#2609)

Nav: Fixed gamepad/keyboard moving of window affecting contents size incorrectly, sometimes leading to scrollbars appearing during the movement. + minor fix with the mostly dead Ctrl+wheel scaling.

Merge branch 'master' into docking ...

# Conflicts:
#	imgui.cpp
#	imgui_internal.h

Internals: Window rectangles: Fixed ContentsRegion lag by moving back after Scrollbar, fixes b50c61c9. Shuffling setup order and added comments.

Internals: Window rectangles: Renaming of all rectangles toward their final form. Should be a no-op. Renamed GetWorkRectMax() to GetContentRegionMaxAbs(). Metrics shows SizeContents.

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

ImDrawList: Added ImDrawCmd::VtxOffset value to support large meshes (64k+ vertices) using 16-bits indices. To enable the feature, the renderer back-end needs to set 'io.BackendFlags |= ImGuiBackendFlags_HasVtxOffset' and honor the ImDrawCmd::VtxOffset field. Otherwise the value will always be zero. This has the advantage of preserving smaller index buffers and allowing to execute on hardware that do not support 32-bits indices. ...

ImDrawList: Added ImDrawCmd::IdxOffset value, equivalent to summing element count for each draw command. This is provided for convenience and consistency with VtxOffset. (#2591)

ImDrawList: Store initial flags for the frame in ImDrawListSharedData, reducing code duplication in setting up the flags.

Internal: Renamed InnerMainRect to InnerVisibleRect. Printing coordinates in Metrics window.

Docking: Fixed DockBuilderRemoveNode() from overwriting other parent node flags when trying to move the CentralNode flag.

Docking: Saving local _NoResize flag. (#2583)

Added full "Dear ImGui" prefix to the title of "Dear ImGui Demo" and "Dear ImGui Metrics" windows. Shortened amount of nodes in columns>tree demo.

Docking: Saving the NoTabBar, NoWindowMenuButton, NoCloseButton fields of dock node into the .ini file. Added them to the Metrics window. (#2583, #2423, #2109).