ISTWCMS-3664: ensuring that contained width is the default for layout builder

source/_patterns/00-config/01-mixins/_mixins.uw.scss

-@mixin uw-contained-width {
-  margin-left: auto;
-  margin-right: auto;
-  max-width: 63rem;
-}
+@mixin uw-contained-width {
+  margin-left: auto;
+  margin-right: auto;
+  max-width: 63rem;
+}
+
+@mixin uw-full-width {
+  max-width: 100%;
+  width: 100%;
+}

source/_patterns/03-layouts/layout/_layout.scss

-.layout.uw-contained-width {
-  @include uw-contained-width;
-}
+.layout {
+  @include uw-contained-width;
+
+  &.uw-contained-width {
+    @include uw-contained-width;
+  }
+
+  &.uw-full-width {
+    @include uw-full-width;
+  }
+}