Fix PVS Studio false positive //-V1020
Fix missing #ifndef for IMGUI_IMPL_OPENGL_LOADER_CUSTOM path

Not intended for frequent calls but I suspect some people will do it either way...
Rough/indicative: measured 0.1 ms for 5000 calls in release, 0.5 ms in debug on my desktop windows.

Backends: OpenGL3: Embed our own minimal GL loader based on gl3w and use it in SDL/GLFW examples. (#4445)

Loader repository at https://github.com/dearimgui/gl3w_stripped
Removed support for using custom loaders in examples/opengl3 backend

Window was not properly hidden in that case.

IO: set io.KeyModsPrev in EndFrame() to tolerate backend writing to io.KeyMods without breaking. (#4439)

Amend ff428f1d

Amend/fix #2445, #2696, #3751, #4377

Nav: Fix not clearing NavWindowingToggleLayer properly (old code left it to true, relied on Alt release only). Removed unnecessary KeyMenu_ from NavInput. (#4439, #787)

Backends: Win32: Fixed keyboard modifiers being reported when host window doesn't have focus. (#2622)

Backends: Win32, SDL, GLFW: only honor io.WantSetMousePos when focused + fix GLFW uninstalling handler + tweaks to reduce branch drift with docking. (#787, #2445, #2696, #3751, #4377)

Backends: Win32: Mouse position is correctly reported when the host platform window is hovered but not focused. (#2445, #2696, #3751, #4377)

Backends: GLFW: Mouse position is correctly reported when the host platform window is hovered but not focused. (#3751, #4377, #2445)

Backends: SDL2: Mouse position is correctly reported when the host platform window is hovered but not focused. (#2445, #3751, #4377)

(requires SDL 2.0.5 because SDL_GetMouseFocus() is only usable with SDL_HINT_MOUSE_FOCUS_CLICKTHROUGH).

(practically speaking it allows me to use StructLayout without hassle)

ImGuiColorEditFlags__DisplayMask > ImGuiColorEditFlags_DisplayMask_, ImGuiColorEditFlags__OptionsDefault > ImGuiColorEditFlags_DefaultOptions_, ImGuiColorEditFlags__DataTypeMask > ImGuiColorEditFlags_DataTypeMask_  etc.

This also removes unnecessary recreation of backend-owned device objects when the window is resized.
+ amend original PR with a g_pSwapChain->SetFullscreenState(false, NULL); call.

Removed unnecessary line in Begin() + commented out redirecting functions/enums names that were marked obsolete in 1.67 and 1.69 + readded commented obsoleted function.

Popups: Fix OpenPopup() being called after BeginPopup() resulting in a failure to open a popup when focus is NULL. (#4308)

Story of removed line begins in commit b80cf0a. It's purpose was to close popups when they lost focus.
Later on few other changes were introduced:
* bcc49ff - closing popups with RMB without changing window focus
* af679a1 - closing popups in FocusWindow()
These two changes covered all the cases of popup closing which made deleted line obsolete. Conveniently, now all popup closing is handled from within UpdateMouseMovingWindowEndFrame() either by calling FocusWindow() or ClosePopupsOverWindow().

Internals: widgets always read back from g.LastItemData.InFlags (so we can now modify per-item disable state more easily). (#211)

(should be a no-op as we are restoring things in Begin/End. Toward faciliate backup/restore of LastItemData and favor pulling from here instead of CurrentItemFlags, toward #211)

Internals: ItemAdd: set LastItemXXX fields before navigation calls + comments about io.IniFilename (#4294)

Disabled: fixed IsItemHovered() if popped disabled state after item, or when using Selectable_Disabled. (#211)

Disabled: items more consistently release active id if the active item got disabled. (#211) (amend 29525255)