feat: add switchable display surfaces for Plot2D (Dock Panel and 3D Overlay)

[sevahul]

Summary

This PR adds a new display-surface mode for Plot2D so users can choose where the plot is rendered:

• Dock Panel
• 3D Overlay

The Dock Panel mode is now the default.

Motivation

The plugin previously rendered only as an in-viewport overlay. This change adds a panel-based presentation mode similar to how image visualization is commonly used in RViz, while preserving the existing overlay behavior.

What Changed

1. Added a new configuration enum and field:

• DisplaySurface
• Stored in Plot2DConfig as display_surface

2. Added a new display property:

• Display Surface
• Options:
  • Dock Panel
  • 3D Overlay

3. Implemented mode switching behavior:

• Live switching between modes while display is active
• 3D Overlay mode:
  • Uses existing overlay backend path
• Dock Panel mode:
  • Renders to a per-display dockable panel widget
  • Supports multiple display instances (one panel per instance)

4. Updated presentation logic:

• Layout controls are hidden when Dock Panel is selected
• Existing series/style/axis/render settings remain unchanged and continue to apply in both modes

5. Added/updated tests for:

• Display Surface property presence and config mapping
• Layout visibility behavior when switching surfaces
• Rendering-path behavior for panel vs overlay

Behavior Notes

• Default surface is Dock Panel.
• Switching to 3D Overlay restores overlay rendering path.
• Switching to Dock Panel hides overlay and renders in the associated dock panel.
• Panel layout persistence follows RViz config save/load behavior.