GLTFLoader: Fix specular-glossiness material.

[Mugen87]

• Fixed the modified lights_physical_fragment shader chunk, see New MeshStandardMaterial in r112 has banding artifacts on some GPUs #18265.
• Fixed the broken usage of tangent-space normal maps. The shader material did not define normalMapType which means TANGENTSPACE_NORMALMAP was never defined.

[Mugen87]

Prod: https://threejs.org/examples/webgl_loader_gltf_extensions.html
PR: https://raw.githack.com/Mugen87/three.js/dev26/examples/webgl_loader_gltf_extensions.html

This is how the boom box looks in prod now:

It also logs the warning:

three.module.js:18258 THREE.WebGLProgram: gl.getProgramInfoLog() WARNING: Output of vertex shader 'vTangent' not read by fragment shader

After this change:

And the warning is gone, too.

[mrdoob]

Thanks!