TSL: Avoid naming collision when using `label()` or `toVar()`.

[Mugen87]

Description

When using label() or toVar() to give variables a name, collisions can occur when the name is already reserved for internal entities like uniforms or varyings.

If you now redefine a variable on app level, a shader error occurs. In WGSL for example:

Error while parsing WGSL: :40:2 error: redefinition of 'cameraNear'

Solution

It would be nice if the node material could automatically detect such name collisions and modify the custom names e.g. with a suffix.

Alternatives

Leave it as it is and ask developers to pick unique names.

Additional context

#29810

[ligaofeng0901]

I have the following thoughts/ideas:

1. .label() is used for uniforms, the names should be detected in shader level. Any uniform generated from a unique node should have a unique name
2. toVar() is used for variables in shader. any variable in a Fn should be visible only in this Fn. Becasue all vars are defined on the top of main function, the name of any variable in a Fn should not collide with any other variables in any other Fns. So far, one situation I meet is

const fn1 = Fn(([param1]) => {
     const var1 = vec3().toVar('var1');
     .....
     return var1;
});

this.colorNode = Fn(() => {
     const var1 = vec3().toVar('var1');
     const a = fn1(1);
     const b = fn1(2);
     .....
     return mix(a, b,  var1);
});

After shader building, the logic of the shader is totally different from what I want. The builder thinks all var1 is the same variable, the value of different var1 will be affected by others.

[sunag]

Fixed here: #30785