CI: Add MinGW build with extra warnings on windows.

(cherry picked from commit ebc98c273054d0f9b305a1346db98052616a8b21)

Internals: Added ImTriangleArea()

Added ability to hover over a draw list's summary stats and see all the contents in wireframe

(cherry picked from commit fd808347bd68a07ad318af6c151028bc9f7b82e7)

Demo: tweaked demo help section, reference to "Examples" and "Tools". Reference to Keyboard navigation. Removed some of the more "obvious/standard" controls.

Internals: Added IM_ASSERT_PARANOID, IMGUI_DEBUG_PARANOID define. Shuffled a bit of the macros section in imgui_internal.h

ImVector: Added shrink() helper. ImFont::RenderText minor optimisation for debug build. Misc: Metrics shows tab names because we now have them.

Added IM_UNICODE_CODEPOINT_MAX. Changed specs of ImFontAtlas::AddCustomRectRegular() (breaking change).

Internals: Using ImU64 for internal ImFile api so we can later wrap them to fseeko/ftello//_fseeki64/_ftelli64 (#2734)

Using in Emscripten example.

Renamed IMGUI_DISABLE_FORMAT_STRING_FUNCTIONS to IMGUI_DISABLE_DEFAULT_FORMAT_STRING_FUNCTIONS. (#1038)
Renamed IMGUI_DISABLE_MATH_FUNCTIONS to IMGUI_DISABLE_DEFAULT_MATH_FUNCTIONS.

Doc comments. Removed .ini parsing code from 1.53 that parsed entries without the [Window] tag (which enabled importing an old .ini file)

Internals: Added GetWindowResizeID(), renamed GetScrollbarID() to GetWindowScrollbarID(). Using integer for resize ID so they matches regardless of the pointer size.
Internals: Renamed IMGUI_USER_ERROR to IM_ASSERT_USER_ERROR().

Misc: Using static_assert() when using C++11, instead of our own construct (avoid zealous Clang warnings).

Error handling: Assert if user mistakenly calls End() instead of EndChild() on a child window. (#1651)
Internals: Moved some error handling code.

Internal: Nav rename preparing for nav inputs ownership changes. IsNavInputPressed() -> IsNavInputTest()

Metrics: Added description to Item Picker.

Scrollbar: Fixed an issue where scrollbars wouldn't display on the frame following a frame where all child window contents would be culled.
Demo: Fixed a small bug with scrolling demo.
Metrics: Tweaks.

TreeNode: Added IsItemToggledOpen() to explicitly query if item was just open/closed, facilitating interactions with custom multi-selections patterns. (#1896, #1861)

TreeNode: The collapsing arrow accepts click even if modifier keys are being held, facilitating interactions with multi-select patterns. (#2886, #1896, #1861)

TreeNode: Reworded code for ImGuiTreeNodeFlags_OpenOnArrow (follow up to f79b2d6c) to make it lightweight. Should be a no-op from user's point of view. Will facilitate using the arrow hovering information in the hot path. (#2886)

Internals: Added ImChunkStream, used by window settings. (more generic followup to 4c13807b, the class will be used more extensively by Tables)

(cherry picked from commit a573943fa0ce323ffb4080e57f5e8fe1bc777c36)

Examples: Emscripten: Removed BINARYEN_TRAP_MODE=clamp from Makefile which was removed in Emscripten 1.39.0 but required prior to 1.39.0, making life easier for absolutely no-one. (#2877, #2878) [@podsvirov]

For more info see: https://github.com/ocornut/imgui/issues/2877

(cherry picked from commit f1772d44be09fd78bf5f1ebda44b39b96180d319)

(cherry picked from commit f2a2be72b341f55c44a035b1257177d83489ea5c)

(cherry picked from commit 14b18697e653de80f75af18113033b2086846194)