feat(material-experimental/mdc-button): support density scaling

Note: mdc-icon-button seems to include the default density styles in their
`mdc-icon-button-without-ripple` mixin. This means that we duplicate density
styles by default. We need to figure out what to do in those cases. It seems like
we need feature targeting for this.

Author: devversion

src/material-experimental/mdc-button/_button-theme.scss

@@ -170,7 +170,14 @@ $mat-button-state-target: '.mdc-button__ripple';
   }
 }
 
-@mixin mat-mdc-button-density($density-scale) {}
+@mixin mat-mdc-button-density($density-scale) {
+  .mat-mdc-button,
+  .mat-mdc-raised-button,
+  .mat-mdc-unelevated-button,
+  .mat-mdc-outlined-button {
+    @include mdc-button-density($density-scale);
+  }
+}
 
 @mixin mat-mdc-button-theme($theme) {
   $color: mat-get-color-config($theme);
@@ -311,7 +318,11 @@ $mat-button-state-target: '.mdc-button__ripple';
   }
 }
 
-@mixin mat-mdc-icon-button-density($density-scale) {}
+@mixin mat-mdc-icon-button-density($density-scale) {
+  .mat-mdc-icon-button {
+    @include mdc-icon-button-density($density-scale);
+  }
+}
 
 @mixin mat-mdc-icon-button-theme($theme) {
   $color: mat-get-color-config($theme);

src/material-experimental/mdc-button/button.scss

@@ -8,7 +8,6 @@
 @include mdc-button-without-ripple($query: $mat-base-styles-query);
 
 .mat-mdc-button, .mat-mdc-unelevated-button, .mat-mdc-raised-button, .mat-mdc-outlined-button {
-  @include mdc-button-density(0, $mat-base-styles-query);
   @include _mat-button-interactive();
   @include _mat-button-disabled();
 }