Breaking Changes in V8

These breaking changes are a result of pull request #1041:

• Simple types, enums and constants have been extracted to the unit VirtualTrees.Types. In case you get a compiler error undeclared identifier, it is usually sufficient to add the unit VirtualTrees.Types to the uses clause. This breaking change will be frequently encountered. For enum you can also turn them into scoped enums.
• The property TVTHeader.Treeview is now of type TCustomControl, you need to cast it e.g. like TVirtualStringTree(Header.TreeView) in case you get an undeclared identifier compiler error in this context.
• The control TVirtualDrawTree has been extracted to its own unit VirtualTrees.DrawTree. In case you get a compiler error undeclared identifier TVirtualDrawTree add the unit VirtualTrees.DrawTree to the uses clause in the interface section.
• TVTHeaderAddPopupItemEvent sender parameter changed to TObject (due to circular references).
• TVTHeaderPopup: TColumnChangeEvent Sender parameter changed to TObject.

There are a few other breaking changes:

• tsUpdating has been removed from, Use function IsUpdating() instead. See issue #1015.
• The property DropTargetHelperSupported and its getter have been removed from the IVTDragManager interface, see issue #1138.
• The flag TVTAutoOption.toAutoChangeScale no longer controls if dpi-scaling takes places, this now happens automatically like in all other VCL controls. If this flag is set, the default node height and the header height are automatically scaled according to the used font. So far, the height was only increased to a minimum width so that the text is not cut off. But the height was never scaled down if the control was moved to a monitor with a smaller scaling. This now happens. See issue #1206.
• The property LineStyle now applies to the tree lines only and is accordingly documented. This fixes issues with VCL theming when drawing grid lines. See issue #1202.
• The official support for RAD Studio XE3 - XE8 has been dropped #1169. Users of these versions of RAD Studio should stay with V7.x.
• The official support for Windows classic mode has been dropped #1173.