Revert most/part of "Shortcut: added Shortcut() function and ImGuiInputFlags in public API + Demo." (#456, #2637)

This reverts commit 0949acb6.

# Conflicts:
#	imgui.h

Needlessly introduced in baae057a from WIP tables branch at the time, ended up unused by Tables.
A comment "I find it counter intuitive that hovering supersedes activation." in #3516 led me to this however this is not the cause of said issue.

InputText: fixed cursor navigation when pressing Up Arrow on the last character of a multiline buffer which doesn't end with a carriage return. (#6000)

Simplify stb_textedit_find_charpos(). Leaving that to simmer for a while before attempting an upstream PR.

Backends: GLFW: Fixed mods state on Linux with Alt-GR text input (e.g. German keyboard layout), (#6034)

Amend 07557674, 1ad8ad62
Ref maybe https://github.com/glfw/glfw/issues/1630

imgui_freetype: fixed a packing issue which in some occurrences would prevent large amount of glyphs from being packed correctly. (#5788, #5829)

This seemingly innocuous change sursingly had very large side-effects of completly breaking packing for the test font mentioned in above issue. Not even sure why tbh. New code matches what stb_truetype's stbtt_PackBegin() does.

Examples: DirectX10, DirectX11: try WARP software driver if hardware driver is not available. (#5924, #5562)

Demo: amend Selectable() + BeginPopupContextItem() demo to maintain and update selection state when popup is open. (#6032)

Backends; Vulkan: do not set VkDescriptorSetLayoutBinding::pImmutableSamplers, allow changing sampler. (#6001, #5502, #914)

Follow up to c9aef160 which removec three funtions worth of duplicate code.

Sampler, descriptor set layout and pipeline layout are created in exact
same way directly in ImGui_ImplVulkan_CreateDeviceObjects(). The removed
functions are local and only has call chain that starts in
ImGui_ImplVulkan_CreateDeviceObjects(), so will always do early return.

Fixes MSVC warning C4390 when /W3 is specified. Reworked from original PR: (void)0 provides better codegen by do-while.
Similar to #5901

Submitted as PR: https://github.com/nothings/stb/pull/1422


Signed-off-by: Neil Bickford <nbickford@nvidia.com>

ScrollToRectEx: Fix bug where scrolling horizontally to an always-centered element that is not visible but could be would take the item's Y coordinate into account.

Neither behavior were used in the codebase for this axis.
Amend 27c58c39 (#5902, #2812, #4242, #2900)
Signed-off-by: Neil Bickford <nbickford@nvidia.com>

Misc shallow merge/sync from docking designed to faciliate cross-merging between docking and string_view.

Tables: fixed matching width of synchronized tables when only some (not all) instances have a vertical scrollbar. (#5920)

Frozen rows (~header) still moving from menu to main layer based on freezing stat.e

Tables, Nav, Scrolling: fixed scrolling functions and focus tracking with frozen rows and columns. (#5143, #4868, #3692)

Internals: tidying up and standardizing outer decoration size storage. (toward #5143, #4868, #3692, #3518)

This is not strictly required presently, but will be consistent with adding inner decoration sizes in next commit, as well as generally being sane.
Locking TitleBarHeight() / MenuBarHeight() values per-window probably have side-effects in ill-defined situation related to changing font size per window.

Internals: reduced duplicate code in CalcNextScrollFromScrollTargetAndClamp() by looping through axiees.

Refactor: moved UpdateAliasKey(), GetMergedModsFromKeys(), UpdateKeyboardInputs(), UpdateMouseInputs() to INPUTS section.

Refactor: moved LockWheelingWindow(), FindBestWheelingWindow(), UpdateMouseWheel() to INPUTS section

Refactor: moved UpdateKeyRoutingTable() to INPUTS section. renamed GetKeyVector2d() -> GetKeyMagnitude2d()

Consider moving to imgui_impl_opengl3_loader.h ?

Fonts: added a 'void* UserData' field in ImFontAtlas, as a convenience for use by applications using multiple font atlases.

+ fixed mislocated Changelog entries added recently.

Fixed cases where CTRL+Tab or Modal can occasionally lead to the creation of ImDrawCmd with zero triangles. (#4857, #5937)

Amend b0a6cd63

This commit is a preparation toward adding ImGui apis with explicit context
and making ImGui applications being able to use multiple context at the same time
whatever their concurrency model.
--
Prior to this commit ImGuiInputTextState::OnKeyPressed was depending on the
global context to know which font and font size to use, and if it should
follow MacOSX behaviors or not (c.f ConfigMacOSXBehaviors).

Instead of using the global context, this commit store the context as
attribute of ImGuiInputTextState. Since this state is forwarded to most
of text edit related function, it possible to access font, font size and
ConfigMacOSXBehaviors from everywhere.

NOTE: I have noticed a bug prior to that commit: if the font or font size
change while editing the same widget, the ImGuiInputTextState become invalid
and there is no code to handle this invalidation. Fixing this bug is out
of scope of current pull request.

# Conflicts:
#	imgui_internal.h