[Enhancement] Articulation Builder: QoL & UX Improvements

[jonathanembleyriches]

Description

This is a collection of quality-of-life improvements aimed at making the Articulation Builder more intuitive and reducing manual setup time.

Proposed Changes

• Smart Naming on Import: Replace the AUTONAME_ prefix for unnamed XML geoms with a cleaner convention (e.g., Geom_[Type]_[Index]) or allow them to inherit names from their parent body.
• Auto-Parenting: Automatically move newly added Sensors and Actuators into their respective DefinitionsRoot folder.
• Class Referencing: Update mj_classname to reference UMJDefaultComponent instead of string referencing.
• Custom Editor Icons: Add unique icons for different MuJoCo types (Geoms, Bodies, etc.) to make the component tree easier to navigate.
• Primitive Materials: Improve UMJPrimitive to properly support and display Unreal Materials for better visual feedback.
• Mesh Geom Component: Create a dedicated component for mesh-based geoms to streamline the workflow when using external assets.
• Editor UI Cleanup: Improve the layout of buttons for running CoACD and toggling simulation options (Editor only).