fix(material/tabs): move unthemable tokens to theme mixin

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)

BREAKING CHANGE:
There are new styles emitted by mat.tabs-theme that are not
emitted by any of: mat.tabs-color, mat.tabs-typography,
mat.tabs-density. If you rely on the partial mixins only and don't
call mat.tabs-theme, you can add mat.tabs-base to get the
missing styles.

src/material/_index.scss

@@ -129,7 +129,8 @@ list-density, list-base;
   stepper-typography, stepper-density, stepper-base;
 @forward './table/table-theme' as table-* show table-theme, table-color, table-typography,
   table-density;
-@forward './tabs/tabs-theme' as tabs-* show tabs-theme, tabs-color, tabs-typography, tabs-density;
+@forward './tabs/tabs-theme' as tabs-* show tabs-theme, tabs-color, tabs-typography, tabs-density,
+  tabs-base;
 @forward './toolbar/toolbar-theme' as toolbar-* show toolbar-theme, toolbar-color,
   toolbar-typography, toolbar-density, toolbar-base;
 @forward './tooltip/tooltip-theme' as tooltip-* show tooltip-theme, tooltip-color,

src/material/tabs/_tabs-common.scss

@@ -215,11 +215,6 @@ $mat-tab-animation-duration: 500ms !default;
     overflow: hidden;
     position: relative;
     flex-shrink: 0;
-
-    @include mdc-tab-indicator-theme.theme(tokens-mdc-tab-indicator.get-unthemable-tokens());
-    @include mdc-tab-theme.secondary-navigation-tab-theme(tokens-mdc-tab.get-unthemable-tokens());
-    @include token-utils.create-token-values(
-      tokens-mat-tab-header.$prefix, tokens-mat-tab-header.get-unthemable-tokens());
   }
 
   .mdc-tab-indicator .mdc-tab-indicator__content {
@@ -352,11 +347,6 @@ $mat-tab-animation-duration: 500ms !default;
 
 @mixin paginated-tab-header-with-background($header-selector, $tab-selector) {
   &.mat-tabs-with-background {
-    @include token-utils.create-token-values(
-      tokens-mat-tab-header-with-background.$prefix,
-      tokens-mat-tab-header-with-background.get-unthemable-tokens()
-    );
-
     @include token-utils.use-tokens(
       tokens-mat-tab-header-with-background.$prefix,
       tokens-mat-tab-header-with-background.get-token-slots()

src/material/tabs/_tabs-theme.scss

@@ -9,6 +9,21 @@
 @use '../core/typography/typography';
 @use '../core/tokens/token-utils';
 
+@mixin base($theme) {
+  .mat-mdc-tab-header {
+    @include mdc-tab-indicator-theme.theme(tokens-mdc-tab-indicator.get-unthemable-tokens());
+    @include mdc-tab-theme.secondary-navigation-tab-theme(tokens-mdc-tab.get-unthemable-tokens());
+    @include token-utils.create-token-values(
+        tokens-mat-tab-header.$prefix, tokens-mat-tab-header.get-unthemable-tokens());
+  }
+  .mat-tabs-with-background {
+    @include token-utils.create-token-values(
+        tokens-mat-tab-header-with-background.$prefix,
+        tokens-mat-tab-header-with-background.get-unthemable-tokens()
+    );
+  }
+}
+
 @mixin color($theme) {
   .mat-mdc-tab-group, .mat-mdc-tab-nav-bar {
     @include _palette-styles($theme, primary);
@@ -77,6 +92,7 @@
 
 @mixin theme($theme) {
   @include theming.private-check-duplicate-theme-styles($theme, 'mat-tabs') {
+    @include base($theme);
     @if inspection.theme-has($theme, color) {
       @include color($theme);
     }