fix(list): density configuration mixins do not account for leading avatars

Currently when someone uses the MDC list w/ evolution styles, it's possible to generate secondary
styles with a different density scale. This can be achieved by using the following mixins:

* `one-line-item-density`
* `two-line-item-density`
* `three-line-item-density`

These mixins currently do not account for leading avatars, unlike they do for icons, checkboxes,
switches, radio's, images and videos. This commit adds code fo leading avatars.

Author: devversion

packages/mdc-list/_evolution-mixins.scss

@@ -883,6 +883,7 @@
 @mixin one-line-item-density($density-scale, $query: feature-targeting.all()) {
   @include _one-line-item-density($density-scale, $query: $query);
 
+  &.mdc-list-item--with-leading-avatar,
   &.mdc-list-item--with-leading-icon,
   &.mdc-list-item--with-leading-thumbnail,
   &.mdc-list-item--with-leading-checkbox,
@@ -900,6 +901,7 @@
 @mixin two-line-item-density($density-scale, $query: feature-targeting.all()) {
   @include _two-line-item-density($density-scale, $query: $query);
 
+  &.mdc-list-item--with-leading-avatar,
   &.mdc-list-item--with-leading-icon,
   &.mdc-list-item--with-leading-thumbnail,
   &.mdc-list-item--with-leading-checkbox,