Improve undoVanillaShading

[SirFancyBacon]

Reworks the undoVanillaShading function to more accurately reverse vanilla shading.

The previous heuristic relied on an artificial cut-off (IGNORE_LOW_LIGHTNESS) that crushed deep blacks into flat blobs and caused artifacting across gradients.

By replacing the old piecewise math with a single, perfectly smooth polynomial curve, we achieved much more accurate global un-shading while simultaneously reducing the CPU overhead per vertex.

Key Changes & Improvements:

• The "Golden" Monotonic Curve: Replaced the old threshold logic with a continuous polynomial curve (11f + (l * 2.2f) - (l * l * 0.012f)).

• Fixes Crushed Blacks: The 11f floor safely lifts the darkest vertices without grouping them together, restoring rich gradients to dark grey objects (like rocks and pillars).

• Flattens Mid-Tones: The 2.2f slope provides the massive lift needed to successfully flatten mid-tone surfaces (like the Falador walls).

• Prevents Artifacting: The gentle 0.012f brake ensures the curve never bends backward (non-monotonic inversion), eliminating the harsh, unnatural shading bands present in previous iterations.

• CPU Optimization: Since this method runs constantly on vertex data, we stripped out expensive operations:

• Replaced division and branching with a single fast inverse square root (1.0f / Math.sqrt(len)).

• Factored out the uniform vanilla light vector (0.577, 0.577, 0.577). Instead of three separate axis multiplications, the engine now sums the normals and performs a single multiplication for the dot product.

• Code Cleanup: Removed the legacy variables (IGNORE_LOW_LIGHTNESS, LIGHTNESS_MULTIPLIER, BASE_LIGHTEN) and the dynamic sun vector matrices that are no longer needed by this unified math profile.

Master/PR:

[SirFancyBacon]

Master/PR(Unlit screens):