fix(material/form-field): move unthemable tokens to theme mixin (#27887)

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)

src/material/form-field/_form-field-theme.scss

@@ -12,7 +12,17 @@
 @use './form-field-density';
 
 @mixin base($theme) {
-  // TODO(mmalerba): Move form field base tokens here
+  @include sass-utils.current-selector-or-root() {
+    @include token-utils.create-token-values(
+        tokens-mdc-filled-text-field.$prefix,
+        tokens-mdc-filled-text-field.get-unthemable-tokens());
+    @include token-utils.create-token-values(
+        tokens-mdc-outlined-text-field.$prefix,
+        tokens-mdc-outlined-text-field.get-unthemable-tokens());
+    @include token-utils.create-token-values(
+        tokens-mat-form-field.$prefix,
+        tokens-mat-form-field.get-unthemable-tokens());
+  }
 }
 
 @mixin color($theme) {

src/material/form-field/form-field.scss

@@ -15,7 +15,6 @@
 @use '../core/tokens/m2/mat/form-field' as tokens-mat-form-field;
 @use '../core/tokens/m2/mdc/filled-text-field' as tokens-mdc-filled-text-field;
 @use '../core/tokens/m2/mdc/outlined-text-field' as tokens-mdc-outlined-text-field;
-@use '../core/style/sass-utils';
 @use './form-field-sizing';
 @use './form-field-subscript';
 @use './form-field-focus-overlay';
@@ -44,24 +43,12 @@
 @include mdc-custom-properties.configure(
   $emit-fallback-values: false, $emit-fallback-vars: false) {
 
-  @include sass-utils.current-selector-or-root() {
-    @include token-utils.create-token-values(
-      tokens-mat-form-field.$prefix,
-      tokens-mat-form-field.get-unthemable-tokens());
-  }
-
   .mdc-text-field--filled {
-    @include token-utils.create-token-values(
-      tokens-mdc-filled-text-field.$prefix,
-      tokens-mdc-filled-text-field.get-unthemable-tokens());
     @include mdc-filled-text-field-theme.theme-styles(
       tokens-mdc-filled-text-field.get-token-slots());
   }
 
   .mdc-text-field--outlined {
-    @include token-utils.create-token-values(
-      tokens-mdc-outlined-text-field.$prefix,
-      tokens-mdc-outlined-text-field.get-unthemable-tokens());
     @include mdc-outlined-text-field-theme.theme-styles(
       tokens-mdc-outlined-text-field.get-token-slots());
   }