Add configurable up axis and iso surface inversion for 3D mesh previews

[Copilot]

Node editor lacked options to match different engine coordinate systems and control iso surface density direction for 3D mesh previews.

Changes

UI Controls

• Add "Up Axis" dropdown: Y-up (default), Z-up (Unreal style), X-up
• Add "Invert Iso Surface" checkbox for Voxel 3D mode
• Both persist across sessions via ImGui settings handlers

Coordinate Transformation

• TransformCoordinates() remaps vertex positions based on selected axis:
  • Y-up: (x, y, z) (no-op)
  • Z-up: (x, -z, y)
  • X-up: (y, z, x)
• Applied to both voxel and heightmap mesh generation

Iso Surface Logic

• IsSolid() wraps density comparison with inversion support:
  • Normal: density <= isoSurface
  • Inverted: density >= isoSurface
• Updated all voxel checks including early-exit optimizations and AO calculations

Implementation

// Before
if( densityValues[noiseIdx] <= buildData.isoSurface ) {
    AddQuadAO(..., Vector3( xf + 1, yf, zf ), ...);
}

// After  
if( IsSolid( densityValues[noiseIdx], buildData.isoSurface, buildData.invertIsoSurface ) ) {
    AddQuadAO(..., TransformCoordinates( xf + 1, yf, zf, buildData.upAxis ), ...);
}

Updated BuildData struct with upAxis and invertIsoSurface fields. Extended AddQuadAO() signature to accept inversion flag for ambient occlusion calculations.

Original prompt

the node editor needs some new configurable options

• ability to change the up axis for 3d mesh previews, so that if the node trees can match outputs in engines with different up axis
• ability to change the iso surface density direction for 3d mesh previews, IE is above or below zero solid

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[Auburn]

Instead of a checkbox have a drop down with a more descriptive text on ISO surface direction.
In the axis rotation add a hover popup with common engine configurations