Fixed crash when appending with BeginMainMenuBar() more than once and no other window are showing. (#2567) + comments

Fixed GCC mem-access warnings (#2565) ...

+ using "if defined" more consistently for Clang.

Fixed ColorEdit breakage introduced by d3a387c (#2557, #1875, #2034)

Fixed InputFloatX, SliderFloatX, DragFloatX functions erroneously reporting IsItemEdited() multiple times when the text input doesn't match the formatted output value (e.g. input "1" shows "1.000"). It wasn't much of a problem because we typically use the return value instead of IsItemEdited() here. (#1875, #2034)

Internal: Renamed fields + minor tweaks (probably shallow break stack-layout pr, sorry!)

Internal: Removed GetNextItemWidth(), relying on ItemAdd or NextItemData.ClearFlags() to clear the width data. Amend 5078fa20 and undo some of its effects of imgui_widgets.cpp

Renamed SetNextTreeNodeOpen() to SetNextItemOpen(). Refactored SetNextItemXXX stuff to match SetNextWindowXXX code closely.

Internal: Storing flags for NextWindowData so that we can clear everything with a single write and remove dummy condition fields.

Internal: Minor tidying/reordering of sections within ImGuiContext / window DC.

Internal: Scrollbar: Further sane simplification (using InnerMainRect instead of duplicating calculations).

Internal: Scrollbar: Extracted scrollbar code for other uses (eg. table v2 scrolling without using a child window).

Separator: Revert 1.70 "Declare its thickness (1.0f) to the layout" change (c5d83d8a). It's not incorrect but it breaks existing some layout patterns. Will return back to it when we expose Separator flags.

Internal: Refactored Separator into SeparatorEx(), exposed ImGuiSeparatorFlags_SpanAllColumns in imgui_internal.h and support without. (#759) + misc comments

Columns: Fixed Separator from creating an extraneous draw command. Fixed Selectable with SpanAllColumns flag from creating an extraneous draw command. (#125)

Version 1.71 WIP + fixed minor typo

Version 1.70

Selectable: With ImGuiSelectableFlags_AllowDoubleClick doesn't return true on the mouse button releas efollowing the double-click. Only first mouse release + second mouse down (double-click) returns true. Likewise for internal ButtonBehavior() with both _PressedOnClickRelease | _PressedOnDoubleClick. (#2503)

Internals: Rename GetContentRegionMaxScreen() -> GetWorkRectMax(). At this point this is mostly useful to facilitate merge of other branches.

Tidying up BeginMenu() code + comments.

Popups: Closing a popup restores the focused/nav window in place at the time of the popup opening, instead of restoring the window that was in the window stack at the time of the OpenPopup call. (#2517) ...

Among other things, this allows opening a popup while no window are focused, and pressing Escape to clear the focus again.

Internals: Added DataTypeApplyOp, DataTypeApplyOpFromText to imgui_internal.h

Internals: Renaming. Renamed ImGuiPopupRef to ImGuiPopupData for consistency and added constructor.

Internals: Exposed ImGuiDataTypeInfo, DataTypeGetInfo(), DataTypeFormatString(). Comments.

Separator: Declare its thickness (1.0f) to the layout, making items around separator more symmetrical.

Nav: Fixed Drag/Slider functions going into text input mode when keyboard CTRL is held while pressing NavActivate.

Internals: TempInputText: Tidying up DragScalar / SliderScalar / TempInputTextScalar.

Internals: TempInputText: Rename InputScalarAsWidgetReplacement() -> TempInputTextScalar(), ScalarAsInputTextId -> TempInputTextId, small tidying up in affected functions.

Internals: Using more explicit PushOverrideID() helper + renamed equivalent internal tree helper.

MenuItem, BeginMenu: Fix undesirable tall frames in horizontal layout context, which would be visible when trying to use rounded selectable/menus. ...

PushStyleVar: Added comments in the assert message.
Minor tweaks.

Misc comments, internal renaming, added disable indentation option to Columns demo section.