Rearrange header comments to find enums easily + fixed inconsistent sorting.

InputText: Improved sturdiness if the ResizeCallback purposefully modify data->BufTextLen or data->BufSize. (#2006, #1443, #1008)

InputText: Fix ResizeCallback callback on restoring initial value with Escape key. Avoid over-allocating for InitialText storage. (#2006, #1443, #1008)

Added optional misc/stl/imgui_stl.h wrapper to use with STL types (e.g. InputText with std::string). (#2035, #2006, #1443, #1008)

InputText: callback InsertChars() support resize callbacks correctly (followup to 24ff259) + fixed demo to use those functions. (#2006, #1443, #1008).

InputText: Fixed a few pathological crash cases on single-line InputText widget with multiple millions characters worth of contents. Because the current text drawing function reserve for a worst-case amount of vertices and how we handle horizontal clipping, we currently just avoid displaying those single-line widgets when they are over a threshold of 2 millions characters, until a better solution is found.

InputText: Fixed not tracking the cursor horizontally When modifying the text buffer through a callback.

ImDrawList: Large text passed to AddText() are being scanned for their end in order to avoid pre-reserving too many vertices.

Internals: InputText: Renaming. Comments.

InputText: Renamed ImGuiTextEditCallback to ImGuiInputTextCallback, ImGuiTextEditCallbackData to ImGuiInputTextCallbackData for consistency. Kept redirection types (will obsolete).

InputText: Added support for buffer size/capacity changes via the ImGuiInputTextFlags_CallbackResize flag. (#2006, #1443, #1008).

InputText: Internal renaming of some fields + final copy uses edit_state.CurLenA+1 instead of buf_size.

InputText: Fixed minor off-by-one issue when submitting a buffer size smaller than the initial zero-terminated buffer contents.

InputText: (Breaking change) removed ImGuiTextEditCallbackData::ReadOnly since it is a duplication of (ImGuiTextEditCallbackData::Flags & ImGuiInputTextFlags_ReadOnly) (#211)

Added IMGUI_VERSION_NUM for easy compile-time testing. (#2025)

Added links to Discourse forums.

Internals: Moved code out of SliderBehaviorT to reduce code bloat and also because caller may have use for the grab_bb for styling purposes.

Internals: Added ImTextCountUtf8BytesFromChar() helper.

SplitterBehavior: Fix for when the sizes are already under the minimum desired size.

Fixed assertion when transitioning from an active ID to another within a group, affecting ColorPicker (broken in 1.62). Made ActiveIdIsAlive track the actual ID to avoid incorrect polling in BeginGroup/EndGroup when the ID changes within the group. (#2023, #820, #956, #1875).

Metrics: Added io.MetricsActiveAllocations, moving away from the cross-context global counters than we previously used. (#1565, #1599, #586)

Nav: NavWindowingList doesn't save to .ini file. TODO entries.

Internals: Extracted RenderMouseCursor() out of EndFrame(). Moved to imgui_draw.cpp along with RenderArrowPointingAt(). Comments. (#2013)

Examples: Cast to ImTextureID instead of void* when assigning to TexId. Applied to all examples. (#2015)

imgui_impl_opengl3: Advertised as a ES2/ES3 renderer. Defaults to ES3 on Android. Default on "#version 300 es" on ES 3. (#2002, #1873)

Nav: Made CTRL+TAB skip menus + skip the current navigation window if is has the ImGuiWindow_NoNavFocus set. (#787) ...

While it was previously possible, you won't be able to CTRL-TAB out and immediately back in a window with the ImGuiWindow_NoNavFocus flag.

Use literals in place of LLONG_MIN, LLONG_MAX ULLONG_MAX if they are not available. Amend 498c0dc. We prefer using the defines if available in limits.h because they somehow tend to work without warnings when enabling strict C++03 compilation. The 3 literals are fallbacks.. (#1926).

Internals: Minor renaming for consistency.

Metrics: Changed io.MetricsActiveWindows to reflect the number of active windows (!= from visible windows), which is useful for lazy/idle render mechanisms as new windows are typically not visible for one frame. ...

Metrics: Added io.MetricsRenderWindow to reflect the number of visible windows.

Using limits.h LLONG_MIN etc. to increase old-compiler compatibility (as ll and ull prefixes were not standard). Not tested much on old compilers, relying on Clang/GCC warnings.