fix(material/divider): move unthemable tokens to theme mixin (#27881)

Though these tokens are not currently affected by the theme, in the
future they will be affected by the design system used for theming (M2
or M3)

(cherry picked from commit 9535454)

src/material/divider/_divider-theme.scss

@@ -5,7 +5,10 @@
 @use '../core/tokens/m2/mat/divider' as tokens-mat-divider;
 
 @mixin base($theme) {
-  // TODO(mmalerba): Move divider base tokens here
+  @include sass-utils.current-selector-or-root() {
+    @include token-utils.create-token-values(
+        tokens-mat-divider.$prefix, tokens-mat-divider.get-unthemable-tokens());
+  }
 }
 
 @mixin color($theme) {

src/material/divider/divider.scss

@@ -1,13 +1,9 @@
 @use '../core/tokens/token-utils';
 @use '../core/tokens/m2/mat/divider' as tokens-mat-divider;
 
-
 $inset-margin: 80px;
 
 .mat-divider {
-  @include token-utils.create-token-values(
-    tokens-mat-divider.$prefix, tokens-mat-divider.get-unthemable-tokens());
-
   display: block;
   margin: 0;
   border-top-style: solid;