Minor tweaks to reduce false positive of PVS Studio static analyzer.

Menus: Tweaked horizontal overlap between parent and child menu (to help convey relative depth) from using style.ItemSpacing.x to style.ItemInnerSpacing.x, the later being expected to be smaller. (#1086)

Added IsItemActivated() as an extension to the IsItemDeactivated/IsItemDeactivatedAfterEdit functions which are useful to implement variety of undo patterns. (#820, #956, #1875)

Internals: EndGroup: Removed unnecesary parameter to ItemSize()

Internals: Removed unnecessary code.

Fonts: Fixed crash if FontGlobalScale is zero. Correctly debug naming default font if not 13 px. Demo: Moved PopupRounding along with other rounding values. Metrics: Displaying indexes with idx to be correct / less misleading.

Internals: Exposed internal SetWindowPos to imgui_internal.h (for imgui-test)

Removed io.DisplayVisibleMin/DisplayVisibleMax (which were marked obsolete and removed from viewport/docking branch already).

Internals: Tracking dummy select scope id (currently always zero) to facilitate merging of the range_select branch. (#1861)

Internals: Track ActiveIdHasBeenPressed (similar to ActiveIdHasBeenEdited). This is currently mostly for the benefit of the range_select branch. (#1861)

Merged from Docking branch: Various small changes, comments, typos fixes, moved blocks. To reduce overall drift. Should be no-op.

InputText: Fixed a bug where ESCAPE would be first captured by the Keyboard Navigation code. (#2321, #787)

imgui-test: Added extra item info callbacks. Using nav_bb for interactions when possible. Comments, Demo tweaks.

ImStrncpy: Fixed -Wstringop-truncation warning on GCC8 (#2323)

Fixed CloseCurrentPopup() on a child-menu of a modal incorrectly closing the modal. (#2308)

Silence XCode static analysis false positive (#2309)

Revert "Added PushID(size_t sz) helper (may not be useful/meaningful for non C/C++ languages)." ...

This reverts commit 20bc06a.

Nav: Removed unnecessary test (always failing).

Using IM_UNUSED() macro.

Fix various XCode and PVS-Studio static analyzer warnings (#2309)

Added PushID(size_t sz) helper (may not be useful/meaningful for non C/C++ languages).

When resizing from an edge, the border is more visible and better follow the rounded corners. Border rendering moved to RenderOuterBorders so it can be called in a different order for docking. (#1495, #822)

Fixed range-version of PushID() and GetID() not honoring the ### operator to restart from the seed value.

Internals: Tweaks. Comments about PushID/GetID public function.

ImHash: Moved crc32 table out of the function so it can be shared, also avoid cases were compiler tries to makes its initialization thread-safe.

avoid floating point exception when _EM_OVERFLOW is enabled (#2303)

ImGuiTextBuffer: Added append() function (unformatted).

Removed trailing spaces (#2038, #2299)

Added checks for "zero-as-null-pointer-constant" warnings for older Clang (#2299, followup to #2277)

Comments about DLL boundaries and using TLS variables for GImGui. (#2292)