[REQUEST] Support for ImGui::DockBuilderAddNode

**Version/Branch of UImGui:**
Version: 5.0.0

**Unity Version**
6000.0.36f

**Render pipeline (HDRP / URP / Built-in)**
Built-in

There are some important functions missing on the ImGui support related to docking such as:
ImGui::DockBuilderAddNode
ImGui::DockBuilderSetNodeSize
ImGui::DockBuilderSplitNode
ImGui::DockBuilderDockWindow