TSL Transpiler: Basic texture support.

[Mugen87]

Related issue: #27538

Description

This PR adds basic texture support to the TSL Transpiler.

Texture nodes are often created with a texture value (meaning an instance of THREE.Texture). To accommodate that, the Transpiler uses placeholders like /* <THREE.Texture> */ when generating calls with texture(), cubeTexture() and texture3D(). For example the following GLSL:

uniform sampler2D diffuseMap;
vec4 color = texture2D(diffuseMap, vec2(0.5, 0.5));

is converted to:

import { texture, vec2, vec4 } from 'three/tsl';

const diffuseMap = texture( /* <THREE.Texture> */ );
const color = vec4( diffuseMap.sample( vec2( 0.5, 0.5 ) ) ).toVar();

That should make it hopefully more clear where users are supposed to pass textures to nodes.