Add DisplayAnchors and Scissor support to DisplayItem

[Copilot]

Checklist

• I have added a changelog entry to the CHANGELOG.md file on the branch/fork (if it is an internal change, this is not needed).
• This pull request meets the Coding Conventions standards: https://github.com/MontyTRC89/TombEngine/blob/master/CONTRIBUTING.md#coding-conventions

Links to issue(s) this pull request concerns (if applicable)

#14

Pull request description

Extends DisplayItem (3D model display objects) with GetAnchors() and scissor clipping so they integrate with DisplayArea the same way DisplaySprite and DisplayString already do.

Changes

• GetAnchors() for DisplayItem — Projects the 3D bounding box into 2D screen space and returns 9 anchor points (corners, edge midpoints, center) in percent coordinates, matching the API of DisplaySprite/DisplayString.
• Scissor support — DisplayItem now stores a scissor rect. ScriptDisplayItem::Draw() captures the active scissor state set by DisplayArea, and Renderer::DrawObjectIn3DSpace() applies/resets it per item.
• Lua registration — GetAnchors bound under the existing ScriptReserved_DisplayStringGetAnchors key.

Usage

local area = TEN.View.DisplayArea(Vec2(10, 10), Vec2(50, 50))
local item = TEN.View.DisplayItem(TEN.Objects.ObjID.PISTOLS_ITEM)

area:AddItem(item)
area:Draw() -- item is now clipped to area bounds

local anchors = item:GetAnchors()
print(anchors.CENTER) -- projected center in percent