Add highPrecisionShader application setting for mobile optimization

[obiot]

Summary

Add a highPrecisionShader boolean to Application settings that controls the default WebGL shader float precision.

• true (default) — uses the highest available precision (current behavior)
• false — forces mediump precision, which is faster on mobile GPUs that support highp but run faster at mediump

Motivation

Mobile GPUs often support highp but execute mediump shaders 2-4x faster in fragment shaders. Currently melonJS auto-detects the highest precision and always uses it. Developers targeting mobile have no way to opt into lower precision for a performance boost without configuring each shader individually.

PixiJS v8 offers preferredFragmentPrecision / preferredVertexPrecision per-shader. A global boolean is simpler and covers the common case.

Implementation

• Add highPrecisionShader: boolean to ApplicationSettings (default true)
• Add to defaultApplicationSettings
• Pass through to the WebGL renderer as settings.highPrecisionShader
• In GLShader constructor, when no explicit precision parameter: use "mediump" if highPrecisionShader === false, otherwise auto-detect via getMaxShaderPrecision()
• The per-shader precision parameter still overrides the global setting

References

• GLShader: src/video/webgl/glshader.js — already accepts precision parameter
• ShaderEffect: src/video/webgl/shadereffect.js — passes precision to GLShader
• getMaxShaderPrecision: src/video/webgl/utils/precision.js