Nav: Minor tweaks also toward removing processing from ItemAdd()

Internal: ItemAdd() minor shallow tweaks

Merge branch 'master' into navigation ...

# Conflicts:
#	imgui.cpp
#	imgui_internal.h

Internal: ItemAdd(), IsClippedEx(): removed unnecessary indirection for ID parameter

Removed extraneous calls to GetCurrentWindowRead() when we already have a ImGuiContext. Internal RenderXXX functions also don't need to write into the Accessed field at all.

Merge branch 'master' into navigation

Nav: Shuffled code in ItemAdd() so that NavProcessItem() may have access to LastItemId (will be required by tabbing)

Nav: Minor midying up and comments,

Nav: Removed possibly redundant test prior to calling NavProcessItem() from ItemAdd()

Nav: Moving code next to its peers

Nav: Moving the big chunk of code from ItemAdd() to NavProcessItem()

Added ActivateItem(), GetItemID() functions.

Nav: Tidying up activation mechanism so that setting NavActivateId can trigger buttons.

ColorButton: Reduced bordering artefact that would be particularly visible with opaque Col_FrameBg and FrameRounding enabled.

TextUnformatted(): minor tweak

Made AlignFirstTextHeightToWidgets() saner and faster (still disliking its name very much!)

Merge branch 'master' into navigation

Nav: Menus and popups now have move request wrap around vertically (using the move request forward thing added recently). (#787)

SetKeyboardFocusHere() added assert to prevent passing values smaller than -1 as we may have to outlaw them (I think nobody was using that)

Removed obsolete comment.

Merge branch 'master' into navigation

Styles: Added ImGuiStyle::ScaleAllSizes(float) helper to make it easier to have application transition to e.g. High DPI with a matching style.

Nav: Added code to render thin highlight type. (#787)

typo

Nav: Highlight clipped within host window then extruded out. (#787)

Nav: Selectable(): activating selectable also sets NavId + removed the MouseDelta test (added in 43ee5d7, #323) as I don't think it is needed. (#787)

Nav: Added NavMoveResultParentId internal info to record when the parent/context of a given NavId. Useful for various algorithms (currently looking at range selection stuff) (#787)

Nav: Added NavJustNavigatedId internal info to record when we land on a given item after a navigation request, useful for various algorithms (currently looking at range selection stuff) (#787)

Changed the internal name formatting of child windows to use slashes as separator, more readable.

Metrics: Draw window bounding boxes when hovering Pos/Size. List all draw layers, trimming empty commands like Render() does.