bug(button-toggle): Mixin does not support color variants

### Is this a regression?

- [ ] Yes, this behavior used to work in the previous version

### The previous version in which this bug was not present was

_No response_

### Description

According to [documentation](https://material.angular.io/guide/theming#using-component-color-variants), the MatButtonToggle component can be stylized using 4 color variants:

> | Component | Supported $color-variant values | Default |
> |--------|--------|--------|
> | Button-toggle | primary, secondary, tertiary, error | secondary |

But when I use the mixin `@include mat.button-toggle-color(theme.$light-theme, $color-variant: primary);` I get the following error:
```
"Invalid color variant: primary. Mixin does not support color variants."
╷
123 │ token-utils.get-tokens-for($tokens, tokens-mat-standard-button-toggle.$prefix, $options...);
│ ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
╵
node_modules\@angular\material\button-toggle\_button-toggle-theme.scss 123:7 -theme-from-tokens()
node_modules\@angular\material\button-toggle\_button-toggle-theme.scss 38:5 color()
src\styles.scss 36:2 root stylesheet
```

### Reproduction

Setup a regular Material 3 project and copy/paste:
```
@use '@angular/material' as mat;

:root {
@include mat.button-toggle-theme($theme);
@include mat.button-toggle-color($theme, $color-variant: primary);
}

```
Replace `$theme` with a M3 theme.

### Expected Behavior

All styles for color variant should be included.

### Actual Behavior

Error is thrown.

### Environment

- Angular: 18.1.3
- CDK/Material: 18.1.3

Start with the button-toggle color() mixin and the _button-toggle-theme.scss locations shown in the stack trace, then reproduce the M3 setup from the issue using src/styles.scss. Trace how the $color-variant option is validated. Done means the primary variant compiles and includes the expected button-toggle styles without the invalid-variant error.

Written by the indexing model from the issue text.