Allow adding and editing custom 3D LUTs

[nroduit]

Is your feature request related to a problem? (optional)

Currently, 3D LUTs (Look-Up Tables) used for volume rendering are fixed and cannot be modified. Users cannot create personalized color/opacity/3D parameter combinations, which limits the flexibility of volume rendering workflows.

Description of the new feature/enhancement

Add the ability to create, copy, and edit custom 3D LUTs directly within Weasis preferences. Default 3D LUTs should always be preserved and read-only, but users should be able to copy any default LUT as a starting point for customization. A custom 3D LUT editor should allow users to define:

• A succession of color mappings
• Opacity transfer functions
• Other 3D rendering parameters (e.g., shading, gradient opacity)
• Grouping of LUT presets by name for easy organization and retrieval

Proposed technical implementation details (optional)

• Introduce a dedicated 3D LUT editor panel from the bottom menu.
• Default LUTs are stored as read-only system resources; copying a default LUT creates a new user-editable entry.
• User-defined LUTs are persisted in the user profile/config directory.
• The editor provides controls for:
  • Color transfer function (color stops with position and RGB values)
  • Scalar opacity transfer function (opacity stops with position and opacity values)
  • Gradient opacity and other 3D-specific parameters
  • According modality
• LUTs can be named and organized into named groups/categories.
• The existing volume rendering view should pick up and display user-defined LUTs alongside the defaults.

Describe alternatives you've considered (optional)

No response

Additional context (optional)

No response