Blender Git Loki

Fix for [#35224] Transform Orientation - order inconsistency

Fix turned out to remove as much "manual UI" from 3D view header as possible. Mode selector and all transform manipulators/orientations stuff are now RNA-based UI (leaving basically only edit mesh select modes with custom handlers, as they have some quite specific features).

To achieve this, four main modifications were done:
* enum-operator-generated menus are now MENU (i.e. dropdown lists) in headers too.
* All bit-flag enums expanded in ROW buttons now have a handling consistent with e.g. layers, or what we already have for transform manipulators, i.e. clicking select only one element, shift-click to select multiple ones.
* Consequently, the three RNA booleans manipulators flags are merged into a single bit-flag enum (yes, this is also an API change, though I doubt many scripts use it).
* Now the width of enum-based dropdown lists is computed from longest item name in enum, no more from a dummy place holder string (when no label/name is given).

All this allows to remove some code from 3DView/transform areas, that was actually mostly duplicating RNA/operator one.

Also done a few optimizations here and there (among others, do not pass &numitems to RNA_property_enum_items() when you do not need it, saves at least an iteration over enum items to count them).

Many thanks to Brecht for the reviews!