theme: Add a couple of generic button styles (#13319)

Author: JosephMcc

data/theme/cinnamon-sass/_widgets.scss

@@ -2,6 +2,7 @@
 @import 'widgets/alttab';
 @import 'widgets/applets';
 @import 'widgets/base';
+@import 'widgets/buttons';
 @import 'widgets/calendar';
 @import 'widgets/desklet';
 @import 'widgets/dialogs';

data/theme/cinnamon-sass/widgets/_buttons.scss

@@ -0,0 +1,21 @@
+.button {
+  @extend %button;
+
+  min-height: 22px;
+
+  &.flat { @extend %flat_button; }
+}
+
+.icon-button {
+  @extend %button;
+
+  border-radius: 9999px;
+  padding: $base_padding;
+  min-height: 16px;
+
+  StIcon {
+    icon-size: 16px;
+  }
+
+  &.flat { @extend %flat_button; }
+}