feat(webgl): add texCoord parameter to getFinalColor hook

[YuktiNandwana]

Resolves #8667

Changes Made

• Updated basic.frag, normal.frag, phong.frag, line.frag to pass texCoord to HOOK_getFinalColor()
• Updated p5.RendererGL.js (4 places) with new hook signature
• Updated WebGPU shaders: color.js, material.js, line.js
• Updated p5.RendererWebGPU.js (3 places) with new hook signature
• Updated JSDoc in p5.Shader.js
• Added visual test (WIP - need help with correct p5.strands syntax for texCoord)

Testing

• All existing tests pass
• 1 pre-existing failure unrelated to this PR
• Visual test added but needs review on correct strands syntax

cc @davepagurek - Could you help verify the correct way to access texCoord in the visual test?