fix(material-experimental/theming): resolve M3 issues in mat-option (#28482)

Fixes the following issues in the M3 `mat-option`:
* Font size was too small and font weight too high. This appears to have been a bug in the spec that MDC is also working around. These changes apply the same workaround as MDC.
* Multi-select options in the selected state had a darker background, even though they shouldn't. This happened to work by accident in M2 and only became visible now in M3.

Author: crisbeto

src/material-experimental/theming/_custom-tokens.scss

@@ -822,9 +822,7 @@
 /// @param {Boolean} $exclude-hardcoded Whether to exclude hardcoded token values
 /// @return {Map} A set of custom tokens for the mat-option
 @function option($systems, $exclude-hardcoded) {
-  @return (mat.private-merge-all(
-    _generate-typography-tokens($systems, label-text, label-large),
-    (
+  @return ((
       selected-state-label-text-color: map.get($systems, md-sys-color, on-secondary-container),
       label-text-color: map.get($systems, md-sys-color, on-surface),
       hover-state-layer-color: mat.private-safe-color-change(
@@ -836,7 +834,17 @@
         $alpha: map.get($systems, md-sys-state, focus-state-layer-opacity)
       ),
       selected-state-layer-color: map.get($systems, md-sys-color, secondary-container),
-    ),
+
+      // According to the spec the options have to be `label-large` in all typography
+      // dimensions, however this is inconsistent with the designs and with MDC's
+      // own implementation. This appears to be a bug in the spec, because MDC overrides
+      // the font size and weight to be `body-large` (see b/261838263). We make the same
+      // override here so the label looks correct.
+      label-text-size: map.get($systems, md-sys-typescale, body-large-size),
+      label-text-weight: map.get($systems, md-sys-typescale, body-large-weight),
+      label-text-font: map.get($systems, md-sys-typescale, label-large-font),
+      label-text-line-height: map.get($systems, md-sys-typescale, label-large-line-height),
+      label-text-tracking: map.get($systems, md-sys-typescale, label-large-tracking),
   ), (
     // Color variants:
     primary: (

src/material/core/option/option.scss

@@ -5,6 +5,7 @@
 @use '@material/typography/typography' as mdc-typography;
 
 @use '../tokens/m2/mat/option' as tokens-mat-option;
+@use '../tokens/m2/mdc/list' as tokens-mdc-list;
 @use '../tokens/token-utils';
 @use '../mdc-helpers/mdc-helpers';
 @use '../style/vendor-prefixes';
@@ -178,6 +179,18 @@
   }
 }
 
+.mat-mdc-option-multiple {
+  // Multi-select options in the selected state aren't supposed to change their background color,
+  // because the checkbox already indicates that they're selected. This happened to work in M2,
+  // due to `list-item-selected-container-color` being the same as `list-item-container-color`,
+  // but that's no longer the case in M3. This overrides ensures that the appearance is consistent.
+  @include token-utils.use-tokens(tokens-mdc-list.$prefix, tokens-mdc-list.get-token-slots()) {
+    $selected-token: token-utils.get-token-variable(list-item-selected-container-color);
+    $base-token: token-utils.get-token-variable(list-item-container-color);
+    #{$selected-token}: var(#{$base-token}, transparent);
+  }
+}
+
 // For options, render the focus indicator when the class .mat-mdc-option-active is present.
 .mat-mdc-option-active .mat-mdc-focus-indicator::before {
   content: '';