Style flat pretty toggle - #8342

This is a further enhancement to PR #7882 & #8014 as discussed in https://community.osarch.org/discussion/3409/surface-styles-revisited
It provides a toggle to switch between prety and flat styles: toggle_prefer_ifc_shading and also a tool to create simple flat shade colors based on the external textures suggest_shade_from_external_style.

• SOLID:

  • Flat (color_type = MATERIAL) Viewport: Solid | Selected Object: None Current Mode: Flat — Shade
  • Flat with object, UV ✓ Viewport: Solid | Selected Object: {name} UV ✓ Current Mode: Flat — Shade
  • Flat with object, UV ✗ Viewport: Solid | Selected Object: {name} UV ✗ Current Mode: Flat — Shade
  • Pretty (color_type = TEXTURE) Viewport: Solid | Selected Object: None Current Mode: Pretty — Texture → Shade
  • Pretty with object, UV ✓ Viewport: Solid | Selected Object: {name} UV ✓ Current Mode: Pretty — Texture → Shade

• MATERIAL_PREVIEW or RENDERED

  • Flat (prefer_ifc_shading = True) Viewport: Material Preview | Selected Object: None Current Mode: Flat — Render+Texture → Render → Shade
  • Flat with object Viewport: Material Preview | Selected Object: {name} UV ✓ Current Mode: Flat — Render+Texture → Render → Shade
  • Pretty (prefer_ifc_shading = False) Viewport: Material Preview | Selected Object: None Current Mode: Pretty — External → Render+Texture → Render → Shade
  • Pretty with object Viewport: Material Preview | Selected Object: {name} UV ✓ Current Mode: Pretty — External → Render+Texture → Render → Shade

Cheers!