fix(material/checkbox): use token for disabled label color

Fixes that we were emitting a concrete style for the checkbox instead of using a token.

Author: crisbeto

src/material/checkbox/_checkbox-theme.scss

@@ -44,11 +44,6 @@
       &.mat-warn {
         @include mdc-checkbox-theme.theme(tokens-mdc-checkbox.get-color-tokens($theme, warn));
       }
-
-      &.mat-mdc-checkbox-disabled label {
-        // MDC should set the disabled color on the label, but doesn't, so we do it here instead.
-        color: inspection.get-theme-color($theme, foreground, disabled-text);
-      }
     }
   }
 }

src/material/checkbox/checkbox.scss

@@ -171,6 +171,11 @@
 
   &.mat-mdc-checkbox-disabled label {
     cursor: default;
+
+    @include token-utils.use-tokens(tokens-mat-checkbox.$prefix,
+      tokens-mat-checkbox.get-token-slots()) {
+      @include token-utils.create-token-slot(color, disabled-label-color);
+    }
   }
 
   // The MDC styles result in extra padding if the label is present but empty. To fix this we hide

src/material/core/tokens/m2/mat/_checkbox.scss

@@ -14,7 +14,9 @@ $prefix: (mat, checkbox);
 
 // Tokens that can be configured through Angular Material's color theming API.
 @function get-color-tokens($theme) {
-  @return ();
+  @return (
+    disabled-label-color: inspection.get-theme-color($theme, foreground, disabled-text),
+  );
 }
 
 // Tokens that can be configured through Angular Material's typography theming API.