fix(material/list): ensure leading icon scales with token

Correct the font size of leading icon in List component. Set font-size of
leading icon to same value as its width and height. Ensure Ensure icon scales to
"list-item-leading-icon-size" token.

Fix icon with cut-off appearance when "list-item-leading-icon-size" is less than
24px.

src/material/list/list.scss

@@ -75,6 +75,13 @@
       @include token-utils.create-token-slot(border-radius, list-item-leading-avatar-shape);
       @include token-utils.create-token-slot(background-color, list-item-leading-avatar-color);
     }
+
+    // Set font-size of leading icon to same value as its width and height. Ensure icon scales to
+    // "list-item-leading-icon-size" token. In Angular Material, the icon is on the same element as
+    // ".mdc-list-item__start", rather than a child of ".mdc-list-item__start".
+    .mat-mdc-list-item-icon {
+      @include token-utils.create-token-slot(font-size, list-item-leading-icon-size);
+    }
   }
 }