Feat/gh1458 possible to drag and drop usages to re-parent them and bumped devexpress to 23.2.15

[rdevoogtatstariongroup]

Prerequisites

• I have written a descriptive pull-request title
• I have verified that there are no overlapping pull-requests open
• I have verified that I am following the COMET-IME code style guidelines
• I have provided test coverage for my change (where applicable)

Description

Move an Element Usage to another Element Definition (drag & drop) — closes #1458

Adds drag-and-drop reparenting of an ElementUsage. Drag a usage onto an
ElementDefinition (in the Element Definitions browser or the Product Tree; in the
Product Tree also onto another usage) and it is moved into that definition —
keeping its Iid, name, short-name, owner, excluded options and all
ParameterOverrides (values included). Previously the only workaround was to
re-create the usage manually, losing all of that.

How

• New IThingCreator.MoveElementUsage(usage, targetDefinition, session) re-parents the
  usage in a single ThingTransaction (same pattern as
  RequirementRowViewModel.ChangeRequirementContainer).
• New shared CDP4Composition/DragDrop/ElementUsageDropValidator centralizes the drop
  guards so both browsers stay consistent and cannot create invalid models:
  write permission, same-model only, and ElementDefinition.HasUsageOf(...) to block
  self-drop and transitive containment loops.
• Wired into ElementDefinitionRowViewModel (EngineeringModel + ProductTree) and the
  ProductTree ElementUsageRowViewModel; a tooltip documents the gesture.

Not included

Duplicating a usage is intentionally left out: the data-source only supports a
server-side copy of an ElementDefinition ("Only Element-Definition may be copied"),
and a client-side deep-create could not reliably restore override values. Tracked
separately (see linked web/SDK tickets); move already preserves everything.

Note for reviewers

This branch also bumps DevExpress 23.2.5 → 23.2.15 across all .csproj to fix the
local NU1605 restore conflict. CI/AppVeyor must serve 23.2.15. Happy to split this
into its own commit/PR if preferred.