docs-bug(ALL): List all CSS Variables

[GrandSchtroumpf]

Documentation Feedback

With @angular/material@15 we can use CSS variable. It would be very useful to list the CSS variable that are available globally (--mdc-theme-primary) and per component (--mat-mdc-form-field-floating-label-scale). Something like Ionic documentation would b great !

Affected documentation page

https://material.angular.io/guide/theming https://material.angular.io/components/:component/api