Blender Git Loki

UI: Support split property layout for pointer search buttons

Pointer search buttons created with `uiItemPointerR()` (which allows
also passing a collection property to search in) did not work with the
split property layout (i.e. `uiLayout.use_property_split`).
For example vertex group search buttons typically use this.

Note that decorators (`uiLayout.use_property_decorate`) are not
supported yet. Although if they are enabled, the decorator column is
still created to keep the layout alignment visually intact. Also re-uses
the existing hack to allow placing multiple items in the row before the
decorator column.

Needed for some in-progress changes to the modifier stack UI.